Country  Life  Education  Series 

FUNGOUS  DISEASES 

OF 

PLANTS 

DUGGAR 


<$> 


Date 


PERSONAL  LIBRARY 
OF 

JOHN  WM.    GREGG 

Value 


THE  LIBRARY 

OF 
THE  UNIVERSITY 

OF  CALIFORNIA 

Landscape  Architecture 

GIFT  OF 
Professor 

Harry  W.  Shepherd 


0 


COUNTRY  LIFE  EDUCATION 
SERIES 

Edited   by  Charles  William   Burkett,  recently   Director 

of  Experiment  Station,  Kansas  State  Agricultural 

College  5   Editor  of  American  Agriculturist 


TYPES  AND  BREEDS  OF  FARM  ANIMALS 
By  Charles  S.  Plumb,  Ohio  State  University 

PRINCIPLES  OF  BREEDING 

By  Eugene  Davenport,  University  of  Illinois 

FUNGOUS  DISEASES  OF  PLANTS 

By  Benjamin  Minge  Duggar,  Cornell  University 

SOIL  FERTILITY  AND  PERMANENT 
AGRICULTURE 

By  Cyril  G.  Hopkins,  University  of  Illinois 

Other  volumes  in  preparation 


FUNGOUS  DISEASES  OF 
PLANTS 


WITH  CHAPTERS  ON 

PHYSIOLOGY,  CULTURE  METHODS 
AND  TECHNIQUE 


BY 


BENJAMIN   MINGE  jDUGGAR 

PROFESSOR    OF    PLANT    PHYSIOLOGY    IN    THE    NEW   YORK   STATE 
COLLEGE    OF    AGRICULTURE,  CORNELL    UNIVERSITY 


GINN   AND   COMPANY 

BOSTON    •   NEW  YORK  •   CHICAGO    .   LONDON 


ENTERED  AT  STATIONERS'  HALL 


COPYRIGHT,  1909,  BY 
BENJAMIN  MINGE  DUGGAR 


ALL    RIGHTS    RESERVED 


8II.I 


idd'l 

NDSCA 
4ITECT 

GIFT 


LANDSCAPE 
ARCHITECTURE 


Cfte   at  ben  gum   jpregg 

GINN  AND  COMPANY  •  PRO- 
PRIETORS •  BOSTON  •  U.S.A. 


PREFACE 


fctRDSCAFB 
ARCH.     f. 

LIBRARY 


It  is  a  noteworthy  fact  that  there  has  been  available  to  student 
and  reader  no  general  text  or  reference  book  of  American  origin 
upon  fungous  diseases  of  plants.  Nevertheless,  for  thirty  years  or 
more  there  has  been  active  investigation  in  this  field,  and  during 
much  of  this  time  instruction  in  plant  pathology  has  been  an 
important  part  of  biological  teaching  in  all  colleges  where  plant 
industry  or  country-life  interests  have  been  adequately  represented. 
In  the  agricultural  colleges  the  teaching  of  general  mycology  has 
been  important,  and  that  of  plant  pathology  is  now  essential.  The 
presentation  should  be  fundamental,  but  it  should  also  bear  a  close 
relation  to  the  affairs  of  life.  Plant  pathological  work  has  been 
rapidly  developed  in  all  countries  characterized  by  a  progressive 
agriculture,  and  for  European  conditions  the  student  experiences 
no  great  lack  of  reference  works. 

Through  the  agricultural  experiment  stations  and  through  the 
extension  work  in  various  states  a  vast  amount  of  information  with 
respect  to  plant  diseases  has  been  published  and  otherwise  dissemi- 
nated, so  that  to  every  intelligent  plant  producer  the  opportunity 
has  been  extended  of  becoming  more  familiar  with  the  crop  rela- 
tions of  destructive  parasitic  fungi.  The  student  and  the  progres- 
sive grower  require  something  further,  and  it  has  therefore  seemed 
none  too  early  to  put  in  book  form  a  comprehensive  discussion  of 
the  chief  fungous  diseases  of  cultivated  and  familiar  plants.  It  is 
not  intended  that  this  book  shall  be  an  introduction  to  systematic 
mycology ;  yet  the  arrangement  of  the  material  in  taxonomic  se- 
quence with  respect  to  the  fungi  largely  eliminates  the  necessity 
of  any  mycological  preparation  as  a  prerequisite. 

As  far  as  practicable,  in  the  discussion  of  each  disease,  three 
important  considerations  have  been  kept  in  view :  (i)  to  describe 
the  pathological  effects  and  other  relations  of  host  and  parasite ; 

V 

761 


vi  PREFACE 

(2)  to  make  clear  the  life  history  of  the  causal  fungus  ;  and  (3)  to 
indicate  the  approved  or  suggested  methods  of  prevention  or  con- 
trol. The  author  fully  recognizes  that  in  any  complete  discussion 
of  a  fungous  disease  there  are  definite  theoretical  subdivisions, 
such  as  symptoms,  pathological  morphology,  etiology,  life  cycle  of 
the  causal  organism,  etc.  Nevertheless,  such  a  system  does  not  at 
present  recommend  itself.  In  the  nomenclature  of  popular  names 
of  diseases  uniformity,  or  special  fitness,  at  a  sacrifice  of  estab- 
lished usage,  has  been  avoided.  An  extensive  host  index  has  been 
included  in  order  to  present  in  a  succinct  form  all  of  the  diseases 
discussed  upon  any  host.  It  is,  perhaps,  needless  to  add  that  the 
chapters  upon  culture  methods,  technique,  and  physiological  rela- 
tions are  designed  primarily  for  reference,  and  to  stimulate  the 
most  complete  use  of  the  available  material.  The  bibliography  is 
intended  to  be  suggestive,  and  the  titles  are  made  prominent  that 
the  suggestion  may  not  be  avoided. 

Aside  from  photographs  and  drawings  made  by  the  author,  the 
illustrations  have  been  derived  from  a  variety  of  sources.  Special 
acknowledgment  is  made  to  Mr.  F.  C.  Stewart,  of  the  New  York 
Agricultural  Experiment  Station,  and  to  Professors  H.  H.  Whetzel 
and  George  F.  Atkinson,  of  Cornell  University,  for  the  privilege 
of  using  many  negatives  from  their  collections.  Many  others  have 
kindly  furnished  material  for  one  or  more  illustrations,  as  credited 
in  the  legends.  In  the  preparation  of  the  drawings  much  assistance 
has  been  given  by  Mrs.  B.  M.  Duggar.  For  helpful  suggestions 
respecting  the  manuscript  and  for  a  first  draft  of  the  synopsis  of 
species  among  the  Uredinales,  the  writer  is  indebted  to  Professor 
George  M.  Reed,  of  the  University  of  Missouri. 

B.  M.  DUGGAR 


CONTENTS 

PAGE 

INTRODUCTION >  -,**•   .    >  .  .     .     .     .  ;l 

PART  I.    CULTURE  METHODS  AND  TECHNIQUE 

CHAI-TER 

I.    ISOLATION  AND  PURE-CULTURE  METHODS 9 

I.  The  Development  and  Application  of  Culture  Methods      .  10 

II.  Cleaning  Glassware .."«'•     .     .  12 

III.  The  Principles  and  Methods  of  Sterilization 15 

IV.  Preparation  of  Culture  Media 23 

Liquid  Media .:,.->•    .    >.    .     .  23 

Solid  Media :-  .:    .    j,     .     .  26 

Neutralization  of  Culture  Media    .     .     .     .     .,;.,..     .  33 

V.   Present  Method  of  isolating  Organisms       ..»_...  34 

II.   TECHNIQUE  OF  FIXING,  IMBEDDING,  AND  STAINING      ...  41 

I.   Fixing .   ';;     .     .  41 

II.  The  Paraffin  Process :   Infiltration  and  Imbedding    ...  45 

III.   Staining       .     ... V:   *  '  ...  4^ 

PART  II.    PHYSIOLOGICAL  RELATIONS 

III.  GERMINATION  STUDIES 55 

IV.  GENERAL  RELATIONS  TO  ENVIRONMENTAL  FACTORS      ...  62 

I.   Saprophytism  and  Parasitism  .     ;  ..     .     .-./.•   ,! .  .     .     .  62 

II.  General  Relations  to  Climatological  Factors 66 

III.  Special  Relations  to  Environmental  Factors 69 

V.   ARTIFICIAL  INFECTION   ....     .?-.     .  V    .     .     .    ",    .     .  76 

VI.   THE  PRINCIPLES  OF  DISEASE  CONTROL  .     .     :     ,     .     . .   .     .  85 

I.   Methods  of  Control *.  •     .;•?/,*     •  85 

II.   Preparation  of  Fungicides  .     .     .     .'.,..     ,.    .     »     .     •  88 

PART  III.    FUNGOUS  DISEASES  OF  PLANTS 

VII.    GENERAL  CLASSIFICATION.     .     .     .     .     .r   .     ..  ;     .:.  »     *     .  93 

I.  Fungous  Diseases  and  Pathology 93 

II.  The  Classes  of  Fungi : .     .     .  94 

VIII.    MYXOMYCETES.    SLIME  MOLDS 97 

I.'Phytomyxales  (Phytomyxaceae) 97 

II.   Club  Root  of  Cabbage  and  Other  Crucifers 97 

vii 


viii  CONTENTS 

CHAPTER  PAGE 

IX.     SCHIZOMYCETES.     BACTERIA        ....-.'.'.,....  103 

I .   Bacteriaceae 1 06 

II.  Black  Rot  of  Cabbage 107 

III.  Wilt  of  Sweet  Corn in 

IV.  Crown  Gall  of  Apple,  Peach,  and  Other  Plants    .     .     .  114 
V.  Olive  Knot,  or  Tubercle-Disease  of  the  Olive  .     .     .     .  1 1 8 

VI.  Bean  Blight      .     .     .     . 119 

VII.   Hyacinth  Disease  .     .    -.•    ;     ..-..?  •. 120 

VIII.  Bundle  Blight  of  Sugar  Cane 120 

IX.   Pseudomonas :   Other  Species  .    :.  ",    -. 120 

X.   Pear  Blight ..-..'.,     .     .     .     .  121 

XI.  Wilt  of  Cucurbits  .     .     .     .     .     .     .     .     :"....  129 

XII.   Soft  Rot  of  Carrot  and  Other  Vegetables 131 

XIII.  Soft  Rot  of  the  Calla.  -.-<•*.     .     .-.     .     ...  133 

XIV.  Wilt  of  Solanaceae      .     .     .     ,:    .-  v    .     v     »     .     .     .  134 
XV.  Bacillus:   Other  Species  .     .     .     .     .     .     ;-   .     .     .     .  134 

X.    PHYCOMYCETES  .     .     .V    .  '  .: ".     .     .-'•"•;•' '•'.-    .     ;     ....  135 

I.  Chytridiales  .     .     .  - ';'' ;  -:.     .  '  .    ';""'  .  '"."    ....  136 

II.   Synchytriaceae  .  •£ --•;•» :-.*     . 136 

III.  Cranberry  Gall .     .     .     / 138 

IV.  Pycnochytrium  Globosum  (Schroet.)  Schroet 139 

V.  Chytridiales:  Other  Species 139 

VI.  Saprolegniales  .     .     .     .     .     »  "  ,V  '.     .     .     .     .     .     .  140 

••^VII.  A  Damping-off  Fungus .     .  '141 

VIII.  Brown  Rot  of  the  Lemon 144 

IX.  Peronosporales .     ."    ,     .     .     .  147 

X.  White  "  Rust "  of  Crucifers       .     .    -  ;V 149 

XI.  Cystopus:  Other  Species    ^    -."'.  -^-; 152 

XII.  Downy  Mildew  of  the  Grape    .     .    >     .     .     ...     .  152 

XIII.  Downy  Mildew  of  the  Cucumber 158 

XIV.  Sclerospora .'»   .     ,.     .     .     .  161 

XV.  Downy  Mildew  of  Crucifers      .     .     .     .     ,-   .     .     .     .  161 

XVI.  Onion  Mildew '.     .     .     .     ...  162 

XVII.   Peronospora :  Other  Species 164 

XVIII.  Downy  Mildew  of  the  Lettuce .     ....     .     .     .     .  164 

XIX.  The  Late  Blight  and  Rot  of  the  Potato 165 

XX.   Downy  Mildew  of  Lima  Beans iji 

XI.     ASCOMYCETES '    .  1 74 

I.  Exoascaceae >     ;  -.&&&.  ~i'   •     -     •  i?5 

II.   Peach  Leaf  Curl     .     .     .     v,  i  t ,  v*;,;j     ., 176 

III.  Plum  Pockets ,     .'   ..     ...  183 

IV.  Witches'  Broom  of  the  Cherry 185 

V.  Helotiaceae  .     .  ..     .     .     ."  :.  ._  .  '.'"•', . "  v"." 185 

VI.  Sclerotinia    .  186 


CONTENTS  ix 

CHAPTER  PAGK 

XI.    ASCOMYCETES  (Continued'] 

VII.  Brown  Rot  of  Stone  Fruits     .     . 187 

VIII.  Gray  Mold,  or  Botrytis  Disease    .     .     .     .     ,    ....  196 

IX.  Lettuce  Drop r    .     .  198 

X.  Stem  Rot  of  Clover 20 1 

XL   Larch  Canker 202 

XII.  Mollisiaceae 203 

XIII.  Alfalfa  Leaf  Spot      .     .     .     . 203 

XIV.  Anthracnose  of  Currants 204 

XV.  .Phacidiaceae    ' 207 

XVI.  The  Black  Spot  of  Maple 208 

XVII.   Perisporiales 209 

XVIII.   Perisporiaceae 209 

XIX.  Root  Rot  of  Tobacco,  Violets,  Peas,  Lupines,  etc.    .  210 

XX.   Sooty  Mold  of  Orange 213 

XXI.  Erysiphaceae 215 

XXII.  The  Gooseberry  Mildew 221 

XXIII.  Mildew  of  Peach.    Rose  Mildew 224 

XXIV.  Mildew  of  Apple  and  Cherry 226 

XXV.   Powdery  Mildew  of  Peas 227 

XXVI.  Mildew  of  Composites  and  Other  Plants    ....  228 

XXVII.  Mildew  of  Woody  Plants 228 

XXVIII.   Powdery  Mildew  of  Grape 229 

XXIX.   Powdery  Mildew  of  Willow  and  Poplar      ....  230 

XXX.  Common  Mildew  of  Trees 231 

XXXI.   Hypocreaceae   .     *;*,'..     .    ., 232 

XXXII.  Wilt  Disease  of  Cotton,  Cowpea,  and  Watermelon  .  233 

XXXIII.  A  Canker  of  Woody  Plants 239 

XXXIV.  European  Apple  Canker 242 

XXXV.   Stem  Rot  of  Sweet  Potato  and  Eggplant   ....  243 

XXXVI.  Ergot      . 244 

XXXVII.  Dothidiaceae 248 

XXXVIII.  Black  Knot  of  Plums  and  Cherries 248 

XXXIX.  Sphaeriales 253 

XL.  Black  Rot  of  Grapes 254 

XLI.  Cranberry  Scald 259 

XLII.  Leaf  Spot  of  Strawberry 261 

XLI  1 1.   Leaf-Spitting  Blight  of  Sugar  Cane 263 

XLIV.  Apple  Scab  and  Pear  Scab 264 

XLV.  Bitter  Rot  of  the  Apple  and  Other  Fruits  ....  271 

XLVI.  Anthracnose  of  Sycamore 278 

XLV II.  A  Disease  of  Young  Oaks 280 

XLVIII.  Bark  Disease  of  Chestnut 281 

XLIX.  Blister  Canker  of  Apple 282 


x  CONTENTS 

CHAPTER  PAGE 

XII.  FUNGI  IMPERFECT: '.     .    .     .'.    r*  .     .     .     .  285 

I.   Hyphomycetes    ....    ••*  •••;':    ;,....     .     .  286 

II.   Melanconiales     .'    .     .     .     .     .     .     .  ;  .    '.     .     .  288 

III.  Sphaeropsidales 289 

IV.  Potato  Scab   .     .     .     .     .     .     .     .     .     .     .     .     .  290 

V.  Bud  Rot  of  Carnations     .    ••„'    ....     .     .     .  293 

VI.  A  Pink  Rot  following  Apple  Scab 295 

VII.  Ramularia      .     .  •  '» •••;/.  '; -  •  I  ;  WV 296 

VIII.  Cercosporella      .     .     /   v   ^-.'•-./    .     *     .     .     .  297 

IX.  Rice  Blast      .     .     .     V'. -v;  ^  •;;./•  v    .     .     .  297 

X.   Polythrincium     ...     .'  ;';. '•'.'"". '"V*  .     .     .  298 

XI.   Peach  and  Apricot  Scab /   .     .     .  299 

XII.  Cladosporium :  Other  Species    .....'..  300 

XIII.  Early  Blight  of  the  Potato     .     .     .     .     . >  .     .     .  301 

XIV.  Onion  Mold  .     ...     .     .     .-    ;     .     .  •  .     .     .  304 

XV.  Macrosporium :   Other  Species 304 

XVI.  Blight  of  Ginseng   .     .     .     .-.     ...     ,     .     .  305 

XVII.  Leaf  Spot  of  Beets      .     ......''...'.     .  309 

XVIII.  Early  Blight  of  Celery      .   -..     .     ; 312 

XIX.  Leaf  Blight  of  Cotton  .     .     .-•,•     ;;.     ;-'.     .     .  313 

XX.  Cercospora:  Other  Species  .     ;     ^     .     .     t    .     .  314 

XXI.  Spongy  Dry  Rot  Fungus  of  Apple 316 

XXII.   Dry  Rot  of  Potatoes 317 

XXIII.  Flax  Wilt 319 

XXIV.  Fusarium:  Other  Species      .     .     .     ./  ;    '.     .     .  320 
XXV.  Root  Rot  of  the  Vine  .     .     .     .;V.^. -,     ,     .     .  321 

XXVI.  Anthracnose  of  Bean  .     .  •*>,/•.     , 322 

XXVII.  Anthracnose  of  Cotton 325 

XXVIII.  Wither-Tip  and  Spot  of  Citrus  Fruits       ...     .  327 

XXIX.  Anthracnose  of  Clover  and  Alfalfa       .     i    V  .-    .  328 

XXX.  Anthracnose  of  Snapdragon  .     .     >-:  .  i   .     .     .     .  329 

XXXI.  Colletotrichum :   Other  Species 330 

XXXII.  Gloeosporium      .-    *•'   ;• 330 

XXXIII.  Anthracnose  of  Grape       .     .     ;  '»     .  :' ;     !     .     .  332 

XXXIV.  Anthracnose  of  Raspberry  and  Blackberry    .     .     .  334 
XXXV.  Glceosporium :  Other  Species 335 

XXXVI.   Marsonia ».*'*$&     •     •  336 

XXXVII.  Peach  Blight      .:/•'......     ......  336 

XXXVIII.  Leaf  Blight  of  Cranberry 338 

XXXIX.   Shot-Hole  Disease  of  Plum  and  Cherry  .  >  .     .     .  339 

XL.  Fruit  Spot  of  Apple 341 

XLI.   Heart  Rot  and  Blight  of  Beets  .     /    .   ' .-    .     .     .  343 

XLII.   Dry  Rot  of  Sweet  Potato     V    /:  i  •  .     .     .'     .     .  344 

XLI  1 1.   Seedling  Stem  Blight  of  Eggplant .     .    ,     .     .     .  345 


CONTENTS  xi 

CHAPTER  PAGE 

XII.  FUNGI  IMPERFECTI  (Continued} 

XLIV.   Phyllosticta .*-....,..,     .     .  345 

XLV.  Black  Rot  of  Sweet  Potato  .     .     .     ,     .     .     .     .     .  348 

XLV.I.  Black  Rot  and  Canker  of  Pomaceous  Fruits     .     .     .  350 

XLVII.   Raspberry  Cane  Blight   .     .     . 354 

XLVIII.  Rose  Leaf  Blotch 357 

XLIX.  Leaf  Spot  cf  the  Pear 358 

L.  Late  Blight  of  Celery 361 

LI.  Septoria:  Other  Species 362 

LI  I.  Currant  Cane  Blight 364 

LI  II.  Leaf  Blight  of  Pear  and  Quince    .     .     .-.     ./  ..     .  365 
LI V.  Sooty  Blotch  and  Fly  Speck  of  the  Apple  and  Other 

Plants ''.'.'    .  367 

XIII.  HEMIBASIDIOMYCETES    .     .     ..*-.»  :  .    „    .   <.    .     .     .     .  370 

I.   Ustilaginales »     ,  •.     .     . ,    .     .  370 

II.  Loose  Smut  of  Oats   .     .     .     ,  . „  .;.<,.'.     . '    .     .  372 

III.  Loose  Smut  of  Wheat     .     .    .-,./,.  -4- ,. •  -  .    . .     .     .     .  375 

IV.  Smut  of  Corn <-...'.  376 

V.  Smut  of  Blue-Stem  Grass •'••.•  37$ 

VI.  Tolyposporium  bullatum  (Schroet.)  Schroet.    .     .     .  378 

VII.  Bunt,  or  Stinking  Smut  of  Wheat     .     ...     .     .     .  379 

VIII.  Tilletia:  Other  Species 380 

IX.  Entyloma -.••.".  >  $'.-:'•  ,'/''•     •     •  380 

X.  Onion  Smut      ......    :.*:.;».','.»     .  381 

XIV.  PROTOBASIDIOMYCETES      .     .     .     .....     .     .     .     .     .     .  384 

I.  Rust  Fungi  .     .     ...     .     -.     .     .     .    '*"'^?.     .     .  384 

II.   Families  and  Genera .':.     .     .     .  388 

III.  Synopsis  of  Species 391 

IV.  Clover  Rust       .     .     .     .;......     ...  ..    .  395 

V.  Rust  of  Beans .     ,     ....  397 

VI.  Rust  of  Vetch  and  Garden  Pea 398 

VII.  Beet  Rust .     *     .     .     .  399 

VIII.   Carnation  Rust 399 

IX.  Uromyces:   Other  Species    .     .     V     .     .     .     *     .     .  402 

X.  Asparagus  Rust 403 

XI.  Violet  Rust 407 

XII.  Mint  Rust .  407 

XIII.  Black  Rust  of  Grain 408 

XIV.  Rust  of  Maize 414 

XV.  Timothy  Rust 415 

XVI.  Brown  Rust  of  Wheat  and  Rye 416 

XVII.  Rust  of  Stone  Fruits 417 

XVIII.  Hollyhock  Rust 419 


xii  CONTENTS 

CHAPTER  PAGE 

XIV.    PROTOBASIDIOMYCETES  (Continued} 

XIX.   Puccinia:   Other  Species 420 

XX.  Gymnosporangium 422 

XXI.  Cedar  Apples  and  Apple  Rust      ........  425 

XXII.   Gymnosporangium:   Other  Species 426 

XXIII.  Orange  Rust  of  Raspberry  and  Blackberry      .     .     .  427 

XXIV.  Rust  of  Roses 430 

XXV.   Rust  of  Rhododendron  and  Norway  Spruce    .     .     .  432 

XXVI.  The  European  Currant  Rust    ....     ^     ...  433 

XXVII.  Orange  Rust  of  Aster  and  Golden-rod  .  : :.     .     .     .  435 

XXVIII.   Rust  of  Poplar      .     ;     .' ;.     .     .     .  437 

XV.     AUTOBASIDIOMYCETES 439 

I.  Exobasidiales 439 

II.  Gall  of  Heaths .     .     .     ;     .     .  440 

III.  Hymenomycetales      ..    ,    '•;  ;;-.  •  '•-.'' 441 

IV.  A  Root  and  Stem  Rot  Fungus 444 

V.  Heart  Rot  of  Sugar  Maple  .     .     .     :  ; 452 

VI.  White  Rot  of  Deciduous  Trees 453 

VII.   Decay,  or  Brown  Rot,  of  Trees 457 

VIII.   Polyporus:   Other  Species 462 

IX.  Fomes .     .     .'.     .     .  464 

X.  A  Brown  Rot  of  Conifers 467 

XI.  Root  Disease  of  Sugar  Cane .     .  469 

XII.  Root  Rot  of  Fruit  Trees 47 1 

XIII.  The  Honey  Agaric 473 

XIV.  European  Root  Disease  of  Alfalfa  and  Other  Plants  477 
XV.  Root  Rot  of  Cotton  and  Alfalfa 479 

HOST  INDEX 4^3 

GENERAL  INDEX 499 


DOWNY  MILDEW  ON  NIAGARA  GRAPES 


FUNGOUS  DISEASES  OF 
PLANTS 


INTRODUCTION 

A  proper  study  of  the  fungous  diseases  of  plants  is  at  once  sci- 
entific and  practical.  The  fungi  were  carefully  studied,  however, 
long  before  their  importance  as  disease-producing  organisms  was 
recognized.  A  history  of  our  knowledge  of  the  fungi  in  general, 
therefore,  takes  us  through  periods  when  the  scientific  and  the 
practical  attitudes  were  not  associated  ;  yet  a  brief  historical  survey 
must  develop  important  and  interesting  facts  bearing  upon  the 
relations  of  scientific  work  to  practical  affairs. 

Systematic  mycology.  A  careful  study  of  the  fungi  as  independ- 
ent groups  of  plants  was  begun  in  the  latter  part  of  the  eighteenth 
century,  and  if  we  examine  the  results  of  the  work  beginning  at 
that  time  and  continuing  into  the  early  half  of  the  nineteenth  cen- 
tury, it  will  be  found  that  this  period  was  one  of  most  accurate 
and  painstaking  endeavor  in  systematic  mycology.  Much  credit  is 
therefore  due  to  the  more  prominent  students  of  that  time,  such 
as  Bulliard,  Persoon,  Nees  von  Esenbeck,  Schweinitz,  Leveille, 
Fries,  and  Berkeley.  The  work  so  well  begun  was  continued  into 
the  second  half  of  the  same  century,  and  among  the  names  particu- 
larly associated  with  that  period  are  those  of  Fuckel,  Karsten,  the 
Tulasne  brothers,  Corda,  and  many  others.  This  systematic  study 
has,  of  course,  continued  to  the  present  time,  although  the  nature  of 
the  work  produced  has  undergone  important  changes.  Two  phases 
in  the  modern  development  of  this  systematic  work  are  well  shown 
by  the  appearance,  on  the  one  hand,  of  Saccardo's  monumental 
"  Sylloge,"  and,  on  the  other  hand,  of  such  complete  morphological 
monographs  as  Thaxter's  "  Laboulbeniaceae." 


2  FUNGOUS  DISEASES  OF  PLANTS 

Physiology  and  morphology.  The  progress  in  systematic  my- 
cology has  made  possible  for  more  than  half  a  century  a  compre- 
hensive study  of  the  diseases  of  plants  ;  yet  systematic  study  alone 
is  not  responsible  for  the  rapid  progress  subsequently  achieved  in 
plant  pathology.  A  number  of  causes  might  be  suggested  as  of 
importance  in  the  development  of  the  latter  field.  It  should  not 
be  overlooked  that  advances  in  general  plant  physiology  were  also 
manifest  at  about  the  beginning  of  the  nineteenth  century,  and 
that  this  phase  of  botany  had  undergone  unusual  development 
toward  the  middle  of  the  century,  under  the  influence  of  Sachs 
and  other  experimentalists  of  his  time.  Again,  a  more  intensive 
method  in  the  study  of  morphology  had  been  introduced,  and  in 
mycology  the  efforts  of  such  men  as  the  Tulasne  brothers  had 
shown  what  could  be  done  in  carefully  following  out  the  life  his- 
tories or  development  of  the  fungi.  Beginning  about  the  middle 
of  the  nineteenth  century,  another  distinctive  epoch  is  entered 
upon,  and  the  developments  of  this  period  are  due  chiefly  to  Anton 
de  Bary  and  his  contemporaries. 

The  rise  of  plant  pathology.  De  Bary  became  the  conspicuous 
leader  in  this  field,  establishing  in  an  incontrovertible  manner  the 
connection  between  the  polymorphic  stages  of  certain  parasitic 
species,  and  the  possibility  of  following,  under  well-controlled  con- 
ditions, the  development  of  little-known  groups.  His  work  was, 
furthermore,  particularly  significant  in  that  he  so  thoroughly  appre- 
ciated the  nature  of  parasitism,  the  epidemic  character  of  fungous 
diseases  of  plants,  and  the  practical  value  of  methods  of  inoculation 
and  infection.  To  him  more  than  to  any  one  else  we  owe  the  influ- 
ence which  directed  future  work  along  the  lines  of  the  most  profit- 
able research.  This  period  witnessed  also  the  advances  made  by 
Pasteur  and  others  in  the  study  of  fermentation  and  disease,  and 
it  was  closely  followed  by  those  perfections  in  the  development  of 
pure  culture  methods  which  have  finally  resulted  in  the  possibility 
of  cultivating  practically  all  bacteria  and  a  very  great  majority  of 
the  fungi.  In  the  study  of  the  fungi  as  the  cause  of  plant  diseases, 
at  this  time,  valuable  service  was  also  done  by  Kiihn,  who  in  his 
early  career  devoted  himself  particularly  to  a  study  of  the  fungous 
parasites  of  cultivated  plants.  The  last  decades  of  the  century  yield 
work  of  such  diversity  and  importance  that  it  is  impossible  here  to 


INTRODUCTION  3 

do  more  than  make  briefest  reference  to  it.  The  work  of  Brefeld 
is  perhaps  most  distinctive,  and  while  his  theoretical  views  have 
not  had  a  host  of  followers,  his  fundamental  studies  in  the  general 
field  of  mycology,  and  particularly,  in  this  connection,  his  wide 
range  of  experiments  in  the  artificial  cultivation  of  organisms,  are 
invaluable.  Among  many  others  who  contributed  special  service  in 
some  phase  of  pathological  or  general  mycological  work  of  that 
time  may  be  mentioned  also  Frank,  Hartig,  Schroeter,  Sorauer,  and 
Winter  in  Germany;  Oudemans  in  Holland  ;  Cornu,  Millardet,  and 
Prillieux  in  France  ;  Comes  in  Italy  ;  Woronin  in  Russia  ;  Eriksson 
in  Scandinavia  ;  Plowright  and  Ward  in  England  ;  Farlow,  Burrill, 
and  many  others  in  the  United  States.  The  work  has  continued 
vigorously,  investigations  and  problems  have  multiplied,  and  with 
adequate  conservatism  the  outlook  is  most  encouraging. 

There  were  some  indications  of  a  plant  pathology  in  existence 
from  the  time  of  the  first  studies  in  systematic  mycology,  but  an 
examination  of  the  books  which  purport  to  be  discussions  of  plant 
pathology  shows  that  they  were  in  large  part  an  attempt  to  classify 
and  suggest  ideas  having  to  do  with  plant  diseases,  after  the  man- 
ner of  the  older  attempts  which  were  made  in  human  medicine.  In 
most  cases  the  life  history  of  the  organism  which  caused  the  disease 
was  entirely  unknown ;  and,  in  fact,  there  is  no  plant  pathology 
which  deserves  the  name  affixed  to  it  prior  to  the  appearance  of 
Kiihn's  "Die  Krankheiten  der  Kulturgewachse,"  Berlin,  1858. 
Between  that  time  and  1900  an  extensive  literature  developed. 
The  status  of  the  morphological  work  is  well  shown  by  De  Bary's 
"  Morphologic  und  Biologic  der  Pilze,"  etc.,  and  in  addition  to  many 
special  life-history  or  monographic  studies  we  have,  from  the  patho- 
logical point  of  view,  such  comprehensive  reference  books  as  those  of 
Comes,  Frank,  Hartig,  Prillieux,  Sorauer,  Tubeuf,  Ward,  and  others. 

Practical  pathology  and  disease  control.  An  important  epoch 
in  the  general  study  of  fungous  diseases  had  its  beginning  in  the 
prevalence  of  grape  diseases  in  France,  which  condition  led  to  the 
discovery  of  Bordeaux  mixture  by  Millardet  in  France  about  1883. 
After  the  severe  tests  to  which  the  copper  mixtures  were  subjected, 
it  became  evident  that  there  was  a  bright  prospect  for  controlling 
many  of  the  fungous  diseases  of  plants,  and  there  developed  therefore 
an  immediate  need  for  plant  pathologists,  or  students  of  fungous 


4  FUNGOUS  DISEASES  OF  PLANTS 

diseases  of  plants,  —  persons  who  should  be,  at  the  same  time, 
appreciative  of  the  problems  of  disease  control.  Incidentally  it  may 
be  noted  that  plant  diseases  were,  for  the  most  part,  understood 
to  be  of  fungous  origin.  In  the  United  States  this  was  more  or  less 
coincident  with  the  organization  of  a  section  of  Plant  Pathology  in 
what  was  then  the  Division  of  Botany  at  Washington,  and  with  the 
development  of  plant  pathological  work  in  many  of  the  state  ex- 
periment stations.  In  a  very  short  time  there  was  unusual  activity 
in  this  study  throughout  the  country.  There  was  also  much  stimulus 
to  the  further  development  of  the  work  in  Europe,  and  the  outcome 
was  that  the  foundations  were  laid  for  a  more  careful  study  of  the 
fungi  from  a  phytopathological  point  of  view.  In  this  country  the 
work  was  directed  more  especially  toward  immediately  practical 
ends,  and  that  which  was  accomplished  within  a  brief  period  of  time 
through  the  efforts  initiated  by  Scribner  and  Galloway  was  remark- 
able. In  more  recent  times  the  work  has  also  been  put  upon  a 
higher  plane,  and  investigations  along  broader  and  more  funda- 
mental lines  have  gone  forward  rapidly  at  many  points  throughout 
the  country,  so  that  to-day  the  extent  of  the  organization  and  equip- 
ment for  research  in  this  field  is  better  than  may  be  found  anywhere 
else  in  the  world.  It  is  perhaps  fortunate  that  this  work  in  the 
United  States  has  developed  in  conjunction  with  the  agricultural 
experiment  stations,  although,  when  the  equipment  in  men,  books, 
and  apparatus  was  new,  many  mistakes  were  made.  This  associa- 
tion of  the  work  insures  that  the  direction  of  it  will  be  at  least 
more  practical  than  if  confined  more  or  less  to  investigations  carried 
on  in  botanical  gardens  or  herbaria.  It  is  perhaps  to  be  regretted 
that  there  cannot  be  more  unity  of  action,  or  cooperation,  in  the 
study  and  control  of  epidemic  diseases.  This,  however,  may  be 
brought  about  in  the  course  of  time. 

Some  aspects  of  modern  plant  pathology.  It  is  very  evident  from 
the  nature  of  the  study,  as  well  as  from  the  historical  notes  which 
have  been  presented,  that  an  analysis  of  the  modern  work  in  plant 
diseases  indicates  several  important  aspects,  which  may  be  grouped 
in  the  following  category  :  (i)  mycological  relations  ;  (2)  anatomical 
effects  ;  (3)  physiological  relations  ;  (4)  control  measures. 

Mycological  relations.  The  mycological  aspect  will  be  concerned 
more  particularly  with  a  minute  investigation  of  the  fungi  from 


INTRODUCTION  5 

systematic,  morphological,  and  physiological  standpoints.  Too  often, 
in  the  early  work,  the  chief  object  of  the  study  has  been  to  identify 
the  fungus  associated  with  a  given  disease  and  to  describe  its  fruit- 
ing stages.  An  investigation  of  the  fungus,  however,  should  include 
an  account  of  its  complete  life  history  wherever  possible,  the  rela- 
tions of  the  fungus  to  conditions  under  which  it  is  injurious,  the 
character  of  the  growth  produced  upon  various  culture  media  (when 
the  organism  is  culturable),  the  conditions  under  which  fruiting 
stages  may  be  developed,  etc.  In  the  course  of  time,  therefore,  it 
will  be  necessary  to  repeat  much  of  the  work  of  earlier  date,  which 
has  seemed  to  be  more  or  less  complete. 

Anatomical  effects.  The  anatomical  study,  in  the  sense  in  which 
it  is  here  used,  will  be  concerned  with  the  relations  of  the  host  to 
the  parasite,  in  so  far  as  the  former  may  be  modified  in  growth  or 
minute  structure.  All  lesions,  hypertrophies,  or  other  structural 
changes  produced  in  the  host  plant  are  worthy  of  the  closest  atten- 
tion. These  changes  in  the  host  are  most  diverse,  varying,  on  the 
one  hand,  from  minute  modifications  of  a  single  cell,  or  of  a  small 
group  of  cells,  to  those  changes  of  form  which  involve  an  immense 
increase  in  the  size  of  the  host  organism,  often  giving  rise  to  rela- 
tively enormous  deformities,  such  as  may  be  noted  in  the  case  of 
the  club  root  of  cabbage,  plum  pockets,  cankers,  and  smut  of  corn. 
Again,  the  deformities  may  result  in  the  pushing  into  growth  of  an 
abnormal  number  of  buds,  in  many  instances  accompanied  by  de- 
creased size  of  the  branches  and  changes  in  the  trophic  relations, 
such  as  to  develop  the  various  forms  of  witches'  brooms.  The 
anatomical  changes1  in  the  host  are  those  most  commonly  termed 
pathological  changes.  Unfortunately  these  are  often  discussed  as 
if  they  were  the  only  pathological  effects.  They  are,  at  any  rate, 
the  chief  evident  pathological  effects  in  many  cases,  and  for  that 
reason  they  constitute  in  the  popular  view  that  which  is  properly 
designated  "  plant  pathology." 

Physiological  relations.  In  close  connection  with  the  anatom- 
ical changes  produced  in  the  host,  a  study  should  be  made  of  the 
physiological  relations  of  host  and  parasite,  particularly  of  the 

1  Kiister  (Pathologische  Pflanzenanatomie,  312  pp.,  121  figs.,  1903)  has  at- 
tempted a  general  classification  of  anatomical  modifications  induced  by  diverse 
stimuli. 


6  FUNGOUS  DISEASES  OF  PLANTS 

physiological  disturbances  in  the  host  itself.1  The  normal  physiology 
of  the  host  requires  attention  in  order  that  a  proper  comparative  study 
may  be  made.  .  The  conditions  which  predispose  the  host  plant  to 
attack,  or,  in  other  words,  the  conditions  favorable  to  the  penetration 
of  the  fungus  and  its  development  within  the  host  are  most  funda- 
mental from  the  standpoint  of  pathology,  and  also  in  order  that 
control  measures  may  be  properly  developed.  It  is  a  direction  in 
which  future  work  promises  most  profitable  returns.  Very  little  of 
lasting  value  has  been  done  towards  determining  the  exact  condi- 
tions under  which  the  host  plant  is  most  susceptible  to  attack.  It 
is  well  known  in  the  case  of  certain  forced  plants  that  the  undue 
suffusion  of  the  plant  with  water,  whether  due  to  lack  of  ventilation 
or  to  a  combination  of  causes,  is  a  certain  factor  in  inducing  disease. 
Under  such  conditions  many  fungi  are  able  to  gain  entrance  and 
become  the  cause  of  epidemics,  whereas,  under  more  normal  con- 
ditions, they  may  remain  as  harmless  inhabitants  of  dead  materials. 

Every  season  shows  differences  in  the  prevalence  of  the  more 
injurious  fungous  diseases.  One  season  the  brown  rot  of  the  peach 
may  affect  only  extremely  sensitive  varieties,  and  the  following 
season  it  may  cause  the  loss  of  those  most  resistant.  Again,  some 
varieties  of  the  host  may  be,  under  most  conditions,  but  slightly 
predisposed  to  attack,  notable  instances  being  those  of  the  very 
slight  predisposition  of  the  Kieffer  pear  to  the  blight,  or  in  the 
resistance  of  certain  American  varieties  of  grapes  to  the  downy 
mildew.  Such  cases  might  be  multiplied  indefinitely,  and,  in  fact, 
there  is  scarcely  a  known  fungous  disease  of  the  variable  cultivated 
crops  with  reference  to  which  all  varieties  of  the  host  plant  are 
equally  susceptible.  This  important  fact  has  led  to  the  selection 
and  to  the  production  through  hybridization  of  varieties  which  shall 
at  once  possess  both  the  qualities  desired  from  the  standpoint  of 
their  own  fruits  or  other  products,  and  which  shall,  at  the  same 
time,  carry  with  them  the  high  resistance  necessary  to  enable  them 
to  compete  with  the  fungous  pests. 

The  effect  of  the  fungus  upon  the  host  may  be,  further,  merely 
to  modify  the  quality  of  the  product,  such  as  the  sugar  or  starch 
content,  without  seriously  affecting  the  appearance  of  the  economic 
product.  In  fact,  the  different  means  whereby  the  effect  of  the 

1  See  Ward,  H.  M.,  Disease  in  Plants,  1901. 


INTRODUCTION  7 

fungus  may  show  itself  in  slight  physiological  disturbances  of  the 
host  are  too  numerous  for  special  consideration. 

Control  measures.  Control  measures  for  the  prevention  of  fun- 
gous diseases  should  be  a  part  of  every  study  which  is  undertaken. 
Reference  has  already  been  made  to  the  very  rapid  development 
of  systematic  methods  of  control.  Control  may  be  developed  along 
one  or  more  very  different  lines.  In  the  first  place,  it  may  concern 
itself  more  particularly  with  a  maintenance  of  the  host  plant  in  a 
"thoroughly  sanitary  environment,  or  in  one  which  renders  it  more 
resistant  to  the  attacks  of  fungi.  It  may  again  concern  itself  with 
the  application  of  deleterious  substances  (fungicides)  to  the  host, 
in  order  that  the  germination  and  growth  of  the  fungous  spores 
may  be  prevented.  This  use  of  fungicides  may  take  the  form  of 
disinfection  of  the  seed  or  of  propagative  parts,  the  application  of 
reagents  to  the  soil  in  order  to  prevent  the  growth  of  the  fungus 
in  the  vicinity  of  the  host  plant,  or  the  application  of  fungicides  to 
the  aerial  vegetative  portions  of  the  host,  which  is  commonly  accom- 
plished by  the  operation  of  spraying.  This  latter  operation  has  been 
practiced  to  a  considerable  extent  for  a  long  period  of  time,  but  the 
really  substantial  development  of  the  work  began  with  the  discovery 
of  Bordeaux  mixture,  to  which  reference  has  already  been  made.  At 
the  present  time  a  great  variety  of  spraying  mixtures  are  employed, 
a  large  number  of  which  contain  copper  compounds,  or  copper 
combined  with  lime,  subsequently  discussed  in  detail.  There  are, 
however,  a  great  many  directions  in  which  the  development  of  de- 
sirable fungicides  may  yet  go  forward.  At  the  present  time  the 
use  of  lime-sulfur  washes  and  sprays  is  rapidly  taking  an  impor- 
tant place.  It  is  particularly  in  connection  with  control  measures, 
or  facts  concerning  the  life  history  of  the  organism  suggesting  such 
measures,  therefore,  that  the  study  of  fungous  diseases  of  plants 
makes  for  itself  a  place  among  practical  sciences.  The  amount  of 
injury  annually  suffered  by  the  various  crops,  due  to  fungous  dis- 
eases, may  be  more  or  less  definitely  ascertained,  and  this  repre- 
sents the  possibilities  to  which  control  work  may  be  pushed.  On 
the  other  hand,  the  relation  of  the  crop  in  unsprayed  regions  to  that 
in  regions  where  spraying  is  used  may  permit  one  more  or  less 
roughly  to  determine  the  actual  saving  through  the  present  imper- 
fect and  rather  haphazard  practice  of  control  measures.  Estimates 


8  FUNGOUS  DISEASES  OF  PLANTS 

which  have  been  placed  upon  the  damage  caused  by  prevalent 
plant  diseases  during  a  single  season  amount  frequently  to  a  very 
considerable  per  cent  of  the  total  value  of  the  crops.  In  the  United 
States  alone  the  destruction  wrought  by  fungous  diseases  is  some- 
times not  far  from  half  a  billion  dollars. 

The  diseases  of  plants  induced  by  other  biological,  physical, 
chemical,  or  mechanical  agencies  are  not  included.  The  lack  of 
plant  nutrients,  or  the  presence  of  particular  nutrients  in  quanti- 
ties sufficient  to  cause  injury,  the  phenomena  commonly  termed 
sunscalds,  wind  effects,  abrasions  due  to  contact,  etc.  are  all  dis- 
turbances which  demand  attention,  but  they  may  have  no  def- 
inite relation  to  epidemic  fungous  diseases,  and  would  therefore 
be  fundamentally  considered  only  in  a  general  treatise  on  plant 
pathology.  On  the  other  hand,  it  is  felt  that  in  connection  with 
any  account  of  the  fungous  diseases  of  plants  it  is  desirable  to 
place  within  easy  reach  of  the  student  certain  related  information. 
In  isolated  chapters,  therefore,  there  is  presented  a  brief  review 
of  culture  methods,  histological  technique,  and  such  facts  of  physi- 
ological significance  as  seem  requisite. 

Culture  methods  are  here  concerned  with  the  essential  steps  in 
preparing  important  nutrient  media  and  means  for  the  isolation 
and  study  of  fungi  in  artificial  cultures.  Such  cultures  are  important 
in  morphological  and  physiological  study,  and  they  afford  in  the 
majority  of  cases  the  only  proper  source  of  spores  or  mycelium  for 
inoculation  purposes. 

Histological  technique  is  requisite  not  merely  to  insure  a  proper 
morphological  study  of  a  fungus  and  its  distribution  in  the  host, 
but  also  in  order  to  make  possible  a  more  comprehensive  analysis 
of  the  tissue  modifications  in  the  host. 

A  discussion  of  special  biological  or  physiological  relations  has 
been  limited  to  a  few  topics.  The  germination  of  spores  is  from 
the  outset  one  of  the  investigational  or  routine  duties  of  the  pathol- 
ogist ;  the  relations  of  the  fungi  to  chief  environmental  factors 
cannot  be  disregarded ;  artificial  infection  is  required  in  determining 
the  causal  organism  ;  and  the  principles  of  disease  control  are  con- 
cerned with  the  immediate  application  of  pathological  study  to 
economic  purposes. 


PART  I 
CULTURE  METHODS  AND  TECHNIQUE 


CHAPTER  I 

ISOLATION  AND  PURE-CULTURE  METHODS 

LOEFFLER,  FR.  Vorlesungen  iiber  die  geschichtliche  Entwickelung  der  Lehre 
von  den  Bakterien  1 :  252pp.  3  pis.  37  figs.  1887.  Leipzig. 

SMITH,  ERW.  F.  Bacteria  in  Relation  to  Plant  Diseases.  Carnegie  Inst.  of 
Washington,  Publication  27  (Vol.  I):  285  pp.  31  pis.  145 figs.  1905. 

(Text-Books  and  Manuals  of  Bacteriology.)  Nearly  all  texts  on  general  bac- 
teriology devote  considerable'space  to  methods  of  culture  work. 


FIG.  i.   VIEW  IN  LABORATORY  EQUIPPED  FOR  PLANT  PHYSIOLOGY  AND 
PATHOLOGY.    (Photograph  by  O.  Butler) 

The  student  who  is  interested  in  the  fungous  diseases  of  plants 
will  find  it  desirable  at  the  outset  to  acquire  a  knowledge  of  pure- 
culture  methods.  The  investigator  in  plant  pathology  can  only  pro- 
ceed confidently  in  his  work  when  he  has  had  practical  training  in 

9 


10  CULTURE  METHODS  AND  TECHNIQUE 

the  cultivation  of  fungi  in  the  laboratory.  This  work  has  become 
increasingly  more  important  in  recent  years.  Laboratory  culture 
methods  were  not  generally  applied  to  a  study  of  the  filamentous 
fungi  until  some  years  after  bacteriology  had  been  revolutionized 
by  a  series  of  important  discoveries  in  this  line  of  technique.  It  is 
at  once  evident  that  the  bacteria  could  never  be  studied  advanta- 
geously except  through  the  establishment  of  pure-culture  methods, 
whereas  the  larger  fungi  were  to  the  early  systematists  and  mor- 
phologists,  organisms  to  be  studied  after  the  method  applied  to  the 
higher  plants  and  animals.  Prior  to  the  new  era  in  bacteriology 
special  methods  were  employed,  it  is  true,  in  the  germination  of 
fungous  spores,  and  some  notable  experiments  in  artificial  infec- 
tion had  been  made.  Nevertheless,  after  the  introduction  of  pure- 
culture  methods  in  general  bacteriological  work  had  become  well 
established,  plant  pathologists  were  not  slow  to  appropriate  and, 
in  certain  directions,  to  develop  a  technique  which  promised  and 
which  has  served  to  throw  open  the  whole  field  of  phytopathology 
to  research  of  a  high  order. 

I.    THE  DEVELOPMENT  AND  APPLICATION  OF  CULTURE 

METHODS 

NOTE.  The  following  are  some  papers  of  interest  in  connection  with  the 
early  development  of  culture  methods. 

KLEBS,  E.    Beitrage  zur  Kenntniss  der  Micrococcen.    Arch.  f.  Exp.  Path.  u. 

Pharmakol  1 :  31-64.    1873. 
COHN,  F.    Untersuch.  iiber  Bacterien.   Beitrage  zur  Biol.  der  Pflanzen  2  :  240- 

276.    1876. 
LISTER,  Jos.    On  the  Lactic  Fermentation  and  Its  Bearings  on  Pathology. 

Trans.  Path.  Soc.  London  29 :  425-467. 
(Dilution  methods  for  obtaining  pure  cultures,  see  p.  445.) 
KOCH,  ROBT.    Zur  Untersuchung  von  pathogenen  Organismen.    Mittheil  a.d. 

Kais.    Gesundheitsamte  (Berlin)  1  :    1-48.  pis.  1-14.    1881. 
(Poured  plate  and  streak  method  first  described.) 
PETRI,  R.  J.    Eine  Kleine  Modification  des   Kochschen   Plattenverfahrens. 

Centrbl.    f.  Bakt.  1  :   279-280.    1887. 
(Description  of  the  now  common  Petri  dish.) 

Rapid  development  in  isolation  technique.  The  most  fruitful 
principles  involved  in  bacteriological  culture  methods  were  the 
outcome  of  work  throughout  not  much  more  than  a  dozen  years, 
practically  between  1873  and  1885.  On  the  other  hand,  the  bio- 
logical facts  encouraging  and  inspiring  investigation  in  this  field 


ISOLATION  AND  FURE-CULTURE  METHODS      1 1 

. 

had  long  been  accumulating.  More  than  a  century  prior  to  the 
dates  mentioned,  Bonnet  and  Spallanzani  showed  some  apprecia- 
tion of  the  principles  of  sterilization  and  they  were  more  or  less 
successful  in  attempting  to  demonstrate  that  when  the  organisms 
in  any  given  nutrient  medium  are  killed,  an  entrance  of  germs 
from  without  is  necessary  in  order  that  growth  may  subsequently 
occur.  Nevertheless,  belief  in  the  infelicitous  idea  of  spontaneous 
generation  gained  strength,  and  was  not  finally  abandoned  by  some 
prominent  scientific  men  until  after  the  great  conquests  made  by 
Pasteur  and  others  in  the  fields  of  fermentation  and  disease.  An 
important  era  was  marked  by  Cohn's  demonstration  that  the  spores 
of  many  bacteria  are  particularly  resistant  to  heat,  and  that  it  is 
only  after  passing  into  the  vegetative  condition  that  boiling  may 
effectually  kill  such  organisms.  This  led  promptly  to  the  adoption 
of  a  discontinuous  method  of  sterilization,  and  thus  it  became  a 
matter  of  easy  manipulation  to  grow  organisms  in  media  rendered 
absolutely  sterile. 

It  was  in  1873  that  Klebs  described  a  "fractional"  method  of 
isolating  bacteria,  and  Lister  five  years  later  developed  a  "  dilu- 
tion "  method.  Viewed  in  the  light  of  to-day  these  methods  were 
burdensome,  yet  they  were  not  impossible  in  the  hands  of  careful 
workers.  The  methods  adopted  were  necessarily  extremely  crude 
in  comparison  with  those  employed  to-day.  The  dilution  process 
was  the  surest  practical  method  of  isolating  yeasts  and  bacteria. 
This  method  consisted  essentially  in  diluting  to  such  extent,  in  the 
beaker  or  other  vessel  of  sterile  water,  a  drop  of  any  fluid  con- 
taining the  organism  so  that  a  drop  of  the  diluted  material  would 
contain,  perhaps,  not  more  than  a  single  cell  or  organism.  This 
dilution  was,  of  course,  based  upon  a  tedious  count  made  under  the 
microscope.  If,  then,  drops  of  this  water  in  which  the  organisms 
or  cells  were  suspended  should  be  transferred  one  to  each  of  sev- 
eral tubes  containing  any  desired  medium,  a  separation  might  be 
effected.  Drops  of  the  liquid  containing  the  organisms  might  also 
be  spread  on  the  surface  of  a  sterile  slice  of  potato,  and,  with  growth, 
separate  colonies  might  appear.  This  was  practically  the  status  of 
methods  which  had  been  developed  for  the  isolation  of  microscopic 
organisms,  up  to  about  1881,  which  date  marks  the  beginning  of  a 
very  distinct  advance. 


12  CULTURE  METHODS  AND  TECHNIQUE 

Isolation  by  means  of  solid  media.  Credit  for  the  sudden  perfec- 
tion of  isolation  methods  is  due  to  Robert  Koch.  He  had  watched 
to  good  advantage  the  difficulties  in  the  way  of  securing  isolated 
colonies  of  bacteria  on  potatoes,  or  by  the  older  methods,  and  in 
search  of  a  more  desirable  medium,  he  began  experiments  in  a 
wholly  new  field.  The  outcome  of  his  researches  was  the  substi- 
tution for  potatoes  of  a  substance  which  would  have  both  liquid  and 
solid  properties.  This  substance  he  found  first  in  gelatin  and  later 
in  agar  agar.  Either  of  these  could  be  employed  in  his  simple  and 
efficient  poured-plate  isolation  method.  The  results  of  those  studies 
have  given  us  a  powerful  equipment  for  the  study  of  the  fungi  as 
well  as  the  bacteria.  The  substitution  of  Petri  dishes  for  plates, 
and  many  refinements  in  the  way  of  sterilization  apparatus  followed 
promptly. 

Mycological  advances.  Meanwhile  valuable  contributions  had 
been  made  by  De  Bary,  Brefeld,  and  others,  serving  to  stimulate 
research  along  purely  mycological  lines.  The  employment  of  syn- 
thesized media,  improvements  in  the  general  methods  of  making 
nutrient  media,  and  the  use  of  diverse  plant  products  have  brought 
into  the  work,  on  the  one  hand,  the  development  of  definite  stand- 
ards, and,  on  the  other,  the  possibility  of  cultivating  forms  once 
prevailingly  thought  to  be  specialized  parasites.  The  recent  devel- 
opment and  application  of  culture  methods  from  the  phytopatho- 
logical  standpoint  has  been  such  as  greatly  to  stimulate  renewed 
interest  in  systematic  mycology,  and  the  physiological  aspect  of  the 
work  has  been  notably  advanced.  In  fact,  the  physiological  studies 
of  the  past  ten  years  have  been  to  a  very  commendable  degree 
studies  in  the  physiology  of  the  fungi.  The  simplicity  of  form,  the 
great  variety  in  species  and  in  habitats,  the  readiness  of  growth  in 
pure  culture,  and  the  rapid  response  to  stimuli  all  unite  to  make 
these  plants  favorable  material  for  investigation  and  demonstration. 

II.    CLEANING  GLASSWARE 

Even  for  ordinary  purposes  in  culture  work  glassware  should  be 
thoroughly  cleaned.  Any  reagents  which  will  conveniently  accom- 
plish the  purpose  may  be  used,  but  the  general  methods  followed 
in  bacteriological  laboratories  are  to  be  advised.  Special  methods 
will  be  necessary  in  certain  cases  and  here  one's  knowledge  of 


ISOLATION  AND  PURE-CULTURE  METHODS         13 

chemistry  must  direct.  Ordinarily  it  is  not  enough  to  depend  upon 
hot  water  and  soap  in  cleaning  glass  vessels.  Petri  dishes,  test 
tubes,  etc.,  may  be  boiled  for  a  short  time  prior  to  cleaning,  and  if 
grease  is  present,  a  small  quantity  of  potash  lye  (about  30  grams 
per  liter)  may  be  added.  If  the  glassware  is  immersed  in  water,  a 
porcelain-lined  vessel  should  be  used,  and  the  latter  may  be  placed 
over  the  flame  or  in  the  steam  sterilizer.  Commercial  hydrochloric 
acid  is  convenient  in  many  cases  for  general  use.  A  chromic  acid 


FIG.  2.   SOME  CHIEF  TYPES  OF  GLASSWARE  REQUIRED  IN  STUDENT  CULTURE 
WORK.    (Photograph  by  Geo.  M.  Reed) 

cleaning  mixture  has  also  become  quite  generally  adopted  and  gives 
excellent  results.  This  mixture  may  be  made  sufficiently  strong  for 
ordinary  purposes  by  dissolving  100  grams  of  potassium  dichromate 
in  1000  cc.  of  hot  water,  then  when  the  salt  is  all  dissolved  and 
the  liquid  cool,  pour  into  it  about  500  cc.  of  strong  sulfuric  acid, 
stirring  constantly.  This  liquid  should  be  stored  in  large-mouthed, 
glass-stoppered  bottles,  and  used  with  care.  It  may  be  used  repeat- 
edly. When  employed,  it  may  act  for  from  ten  minutes  to  twenty- 
four  hours,  and  it  may  be  followed  by  water,  or  soap  and  water, 
etc.  This  mixture  is  not  convenient  to  handle  but  is  very  effective. 
Test  tubes.  Ordinarily  these  should  be  cleaned  with  hot  water, 
soap  and  a  test  tube  brush  ;  and  this  cleaning  may  be  preceded  or 


14  CULTURE  METHODS  AND  TECHNIQUE 

followed  by  the  potash  solution  or  the  cleaning  mixture,  as  occasion 
may  demand.  In  either  case  the  tubes  are  thoroughly  rinsed  ulti- 
mately with  distilled  water,  the  outside  of  each  wiped  dry,  and 
they  are  then  placed  upon  a  test  tube  rack.  In  order  that  they  may 
dry  rapidly  and  without  blemish,  they  may  be  rinsed  with  95  per 
cent  alcohol.  A  considerable  quantity  of  alcohol  may  be  used  in 
the  first  tube,  the  top  of  which  when  shaken  is  closed  with  the 
finger.  The  same  alcohol  may  thus  be  used  for  twenty  or  more 
tubes  successively.  Tubes  containing  agar,  or  old  cultures,  are  more 
easily  cleaned  after  being  boiled  for  some  time  in  the  steam  steril- 
izer or  in  the  autoclave. 

Petri  dishes.  These  are  generally  cleaned  with  hot  water  and 
soap.  They  should  be  thoroughly  rinsed  in  clean,  hot  water  and 
wiped  while  yet  hot.  It  is  seldom  necessary  to  leave  cultures,  or 
the  agar  employed  in  cultures,  in  these  dishes  until  the  medium 
becomes  hard  and  dry.  If  so,  it  may  be  essential  to  soak  or  steam 
the  dishes  a  long  time  before  cleaning. 

Flasks.  It  is  difficult  to  get  at  the  interior  of  flasks  with  any 
type  of  brush,  whereas  reagents  are  readily  .employed  in  cleaning 
such  apparatus.  The  chre|nic  acid  mixture  should  then  be  employed, 
and  afterwards  the  flasks  are  rinsed  and  treated  with  alcohol  as  for 
test  tubes.  If  the  flasks  are  desired  for  immediate  use,  after  the 
alcohol  treatment,  they  should  be  rinsed  with  a  small  quantity  of 
ether,  and  may  then  be  rapidly  dried  with  a  blast  or  foot  bellows, 
if  one  is  convenient. 

Slides  and  cover  glasses.  When  new,  or  when  stained,  these 
may  be  effectively  cleaned  by  the  chromic  acid  mixture,  in  which 
they  should  remain  from  twelve  to  twenty-four  hours.  They  are 
next  rinsed,  and  the  slides  wiped  directly,  while  the  covers  should 
be  wiped  with  cheese  cloth  or  linen  after  a  transfer  to  alcohol. 
When  the  slides  are  soiled  with  paraffin,  wax,  vaseline,  or  other 
oily  material,  boiling  in  the  potash  solution  or  in  carbonate  of  soda 
will  be  necessary.  The  same  treatment  should  be  used  for  tubes 
sealed  with  paraffin.  Balsam  preparations  are  cleaned  by  soaking 
for  some  time  m  75-90  per  cent  alcohol,  and  then  by  rinsing  in 
waste  xylol,  benzine,  or  other  such  solvent  of  the  balsam. 

Special  methods.  For  studies  in  nutrition,  germination  experi- 
ments with  special  stimuli,  and  other  very  careful  physiological 


ISOLATION  AND  PURE-CULTURE  METHODS         15 

work,  it  is  necessary  to  have  glassware  which  is  not  only  clean  with 
relation  to  extraneous  substances,  but  which  is  as  far  as  possible 
free  from  the  soluble  substances  which  may  be  contained  in  the 
glass  itself.  In  the  first  place,  it  is  well  to  have  vessels  of  Jena  or 
of  the  best  Bohemian  glass.  Such  glassware .  may  be  first  cleaned 
by  the  ordinary  process.  This  is  followed  by  boiling  in  the  potash 
or  other  alkaline  solution.  The  vessels  are  then  rinsed  and  boiled 
in  weak  hydrochloric  acid,  and  rinsed  again.  Finally,  they  are  filled 
with  distilled  water  and  steamed  for  a  number  of  hours. 

In  this  connection  it  may  be  said  that  cover  glasses  which  have 
been  perfectly  cleaned  and  dried  will  give  more  trouble  in  the 
preparation  of  hanging  drop  cultures  than  those  less  perfectly 
washed.  On  the  former  there  is  a  tendency  for  the  drop  to  spread 
or  to  shift  its  position  at  the  slightest  movement.  Loss  of  stability 
in  the  drop  should,  however,  be  sacrificed  to  absolute  cleanliness 
if  one  is  doing  quantitative  work.  The  drop  will  have  even  a 
greater  tendency  to  spread  if  the  cover  glasses  are  flamed  imme- 
diately before  being  used.  To  avoid  this  latter  difficulty,  if  wiped 
with  a  clean  sterilized  linen  cloth  and  placed  in  a  sterile  Petri  dish 
just  as  they  are  taken  from  the  alcohol,  there  will  be  practically  no 
danger  of  contamination. 

Cover  glasses  which  are  to  be  used  in  making  preparations  of 
bacteria  should  be  absolutely  clean,  and  the  method  above  mentioned, 
namely,  boiling  in  an  alkali,  in  acid,  and  in  distilled  water  is  requi- 
site. They  should  be  air-dried  from  strong  alcohol.  Thus  prepared, 
the  covers  will  permit  the  operator  to  spread  uniformly  over  the 
surface  a  drop  containing  bacteria. 

III.    THE  PRINCIPLES  AND  METHODS  OF  STERILIZATION 

Vessels  and  media.  Sterilization,  as  the  term  is  generally  em- 
ployed, is  merely  the  process  of  killing  all  of  the  organisms  or 
spores  which  may  be  present  in  a  medium  or  vessel  or  upon  a 
given  object.  In  culture  work  sterilization,  therefore,  is  more  par- 
ticularly employed  when  a  substance  or  vessel  is  to  be  used  for 
the  culture  of  a  particular  organism,  or  to  preserve  nutrient  media 
from  decomposition.  The  common  and  most  effective  method  of 
sterilization  is  by  means  of  heat.  Some  important  uses  of  chem- 
ical agents  in  sterilizing  are  not  here  considered.  Steam  heat  or 


1 6  CULTURE  METHODS  AND  TECHNIQUE 

dry  heat  may  be  used,  depending  upon  the  nature  of  the  medium 
or  object  to  be  sterilized.  Liquids  or  any  solids  which  may  melt, 
evaporate,  or  dry  out  in  a  dry  atmosphere  require  moist  or  steam 
heat ;  while  all  heat-resistant  dry  apparatus  and  glassware,  and  well- 
dried  solids,  such  as  sand,  glass  wool,  etc.,  usually  require  dry  heat. 
Sterilization  at  IOO°  C.  When  steam  heat  is  used,  sterilization 
is  often  given  at  the  boiling  point  of  water.  Sterilization  may  thus 


FIG.  3.  ON  THE  RIGHT,  ARNOLD  STEAM  STERILIZER;  ON  THE  LEFT,  LAUTEN- 
SCHLAGER  HOT  AlR  STERILIZER  ;  BOTH  UNDER  HOOD 

be  effected  in  an  ordinary  boiler,  or  over  a  water  bath.  Steam 
sterilizers  of  various  patterns  are  now  made,  which  accomplish  this 
work  most  effectively,  and  they  should  be  in  use  in  all  laboratories. 
The  two  general  types  of  sterilizers  in  common  use  are  those 
which  bear  the  name  of  Koch  and  Arnold.  The  latter  are  simpler 
in  design  and  less  expensive.  Fig.  3  shows,  a  good  form  of  this 
sterilizer.  From  the  diagram,  Fig.  4,  it  will  be  seen  that  the  water 


ISOLATION  AND  PURE-CULTURE  METHODS 


in  the  chambered  bottom  is  rapidly  brought  to  the  boiling  point, 
and  then  the  gradual  entrance  through  the  holes  of  water  from  the 
reservoir  will  supply  the  boiler  for  several  hours,  if  it  is  necessary 
to  employ  it  so  long. 

The  Koch  sterilizer  is  now  less  used.  Aside  from  being  a  well- 
made  piece  of  apparatus,  it  has  only  the  advantage  that  the  regulation 
of  the  water  supply  is  automatic. 
It  is  expensive  and  is  only  espe- 
cially desirable  in  case  of  steriliza- 
tion or  digestion  for  many  hours. 

Countless  experiments  have 
shown  that  while  the  vegetative 
cells  of  most  bacteria  are  usually 
killed  by  a  single  sterilization  of 
from  fifteen  minutes  to  one  hour 
dt  1 00°  C.,  yet  the  spores  of  many 
forms  are  not  killed  by  one  ex-  FIG.  4.  ARNOLD  STEAM  STERILIZER, 
posure  at  this  temperature.  As  a  SQUARE  TvpE' SHOWING  CONSTRUC- 

r      r  'r  TION 

matter  ot   tact,  an  exposure   for 

a  few  minutes  at  100°  C.  in  the  steam  sterilizer  is  usually  suffi- 
cient to  kill  the  growing  parts  of  most  fungi.  It  is  not,  however, 
such  delicate  parts  which  are  to  be  reckoned  with  in  the  sterilization 
of  nutrient  media,  but  rather  the  resistant  spores  of  fungi  and  bac- 
teria, and  thick-walled  mycelial  parts.  Forms  which  are  strongly 
heat-resistant  may  often  be  encountered  in  the  preparation  of  such 
media  as  potatoes  and  manure  decoction. 

To  Cohn  is  due  the  notable  discovery  of  heat-resistance  in  the 
cpores  of  bacteria,  and  logically  following  this  Tyndall  demonstrated 
the  necessity  of  discontinuous  or  successive  sterilization,  after  in- 
tervals sufficiently  long  to  permit  such  organisms,  or  parts  of  organ- 
isms, as  have  remained  as  spores  to  germinate,  and  therefore  to  be 
more  readily  killed  at  the  next  heating.  In  general,  it  is  necessary 
to  sterilize  on  three  successive  days.  As  is  well  known,  when  one 
13  careful  in  making  the  medium  a  single  sterilization  of  half  an 
hour  is  usually  sufficient  for  tubes  of  agar,  if  the  apparatus  has 
not  become  infested  with  particularly  resistant  spores.  In  no  case, 
however,  should  one  depend  upon  a  single  sterilization  unless  the 
material  is  to  be  kept  several  days  previous  to  inoculation.  Stock 


1 8  CULTURE  METHODS  AND  TECHNIQUE 

quantities  of  media  should  be  sterilized  three  times.  Between  the 
periods  of  sterilization  media  should  be  placed  at  a  temperature 
favorable  for  most  bacterial  development,  and  not  in  a  cold  place, 
this  being  in  order  that  any  spores  might  pass  into  the  vegetative 


FIG.  5 a.  AUTOCLAVE,  ERECT  TYPE,  CLAMPED  TOP,  HEATED  BY  GAS 
(Photograph  by  Geo.  M.  Reed) 

state  within  twenty-four  hours,  and   thus   be   killed   at  the   next 
sterilization. 

A  suggestion  which  has  been  made  by  Theobald  Smith  is  of 
interest  in  connection  with  the  sterilization  of  media  which  may  con- 
tain anaerobic  bacteria.  If  such  media  are  sterilized  in  thin  layers, 
oxygen  may  have  comparatively  free  access  to  any  submerged 


ISOLATION  AND  PURE-CULTURE  METHODS         19 

spores,  and  consequently  they  may  not  germinate  between  the 
successive  sterilizations.  On  the  other  hand,  if  the  medium  is 
deep  in  the  vessel,  and  the  exposed  surface  of  the  medium  small, 
much  less  oxygen  gains  access,  and  the  spores  of  anaerobic  forms 
pass  more  readily  into  the  vegetative  condition  and  are  killed  by 
the  successive  sterilizations. 

Sterilization  under  pressure.    A  great  time-saving  convenience 
in  sterilization  is  to  be  found  in  the  use  of  the  autoclave,  or  steam 


FIG.  53.   AUTOCLAVE,  HORIZONTAL  TYPE,  CONNECTED  WITH  STEAM  PIPES 
(All  steam  apparatus  under  a  hood) 

pressure  sterilizer,  two  types  of  which  are  shown  in  Fig.  5,  a  and  b. 
The  autoclave  is  not  only  more  effective  than  the  ordinary  steam 
sterilizer,  but  by  using  it  the  delay  of  discontinuous  sterilization  is 
avoided.  In  this  apparatus  the  steam  is  confined,  up  to  any  pres- 
sure desired,  instead  of  being  allowed  to  escape,  as  in  the  ordinary 
steam  sterilizer.  A  good  steam  pressure  gauge  on  the  autoclave 
is  requisite,  and  a  thermometer  is  not  only  desirable,  but  also  an 
additional  safeguard.  The  temperature  ordinarily  employed  is  115° 
to  125°  C.,  or  about  10  to  20  Ibs.  pressure.  A  single  incubation 


20  CULTURE  METHODS  AND  TECHNIQUE 

of  from  fifteen  to  twenty  minutes  at  this  temperature  will  usually 
sterilize  any  medium.  The  period  of  incubation  must  of  course  be 
measured  from  the  time  the  desired  temperature  is  attained,  and  it 
may  require  from  ten  to  fifteen  minutes,  even  with  a  strong  burner 
system,  in  order  to  reach  this  temperature.  An  autoclave  contain- 
ing an  ordinary  amount  of  culture  vessels  should,  if  provided  with 
a  double  ring  of  burners,  and  jacket,  develop  a  pressure  of  15  Ibs. 
in  about  ten  minutes. 

Temperatures  higher  than  115°  may  transform,  possibly  through 
acidity,  many  sugar-containing  and  other  organic  media,  and  con- 
sequently greatly  reducing  their  value  for  the  growth  of  many 
organisms.  Gelatin  and  milk  are  injured,  if  acid,  by  autoclave  tem- 
peratures. With  more  readily  decomposable  substances  sometimes 
necessarily  employed  in  phytopathological  work,  it  may  be  possible 
to  effect  sterilization  at  temperatures  below  the  boiling  point,  at 
from  80°  to  90°  C.,  say,  sterilization  being  made  on  about  six  suc- 
cessive days.  The  blood  serum  incubator  may  also  be  employed. 

Not  only  does  the  autoclave  facilitate  sterilization,  but  it  is  eco- 
nomical in  the  preparation  of  media  to  such  an  extent  that  it  should 
be  in  general  use.  The  expense  of  such  a  piece  of  apparatus  is  the 
one  factor  operating  against  its  general  adoption,  yet  a  good  instru- 
ment handled  carefully  should  last  a  number  of  years. 

The  autoclave  may  be  heated  by  burners,  or  it  may  be  connected 
with  a  steam  supply  pipe,  if  a  supply  of  steam  under  sufficient 
pressure  may  be  constantly  at  hand.  Autoclaves  are  usually  pre- 
pared for  gas  burners.  In  using  this  instrument  care  should  be 
taken  to  arrange  mechanical  reminders  if  there  is  danger  of  its 
being  neglected  even  for  half  an  hour.  It  might  be  suggested  that 
an  alarm  clock  as  such  is  useful,  or  that  a  clock  arrangement  for 
shutting  off  the  gas  at  the  desired  time  is  in  use  in  some  labora- 
tories. With  the  gas-heated  autoclaves,  particularly,  certain  precau- 
tions are  necessary.  Before  each  sterilization  it  must  be  noted  that 
sufficient  water  is  present,  usually  up  to  the  crate  or  false  bottom ; 
and  it  is  well  to  employ  distilled  water.  The  lid  and  other  fittings 
should  be  kept  free  of  dirt  and  dust,  so  that  all  fastenings  may  be 
tight  and  secure.  If  the  burner  capacity  is  not  too  great,  the  gauge 
screw  may  with  little  practice  be  set  at  the  temperature  desired,  the 
steam  vent  left  open,  and  the  apparatus  lighted.  A  few  minutes  after 


ISOLATION  AND  PURE-CULTURE  METHODS         21 

steam  begins  to  escape  vigorously,  or  practically  as  soon  as  the 
thermometer  registers  100°  C.,  the  vent  is  closed.  It  is  not  advis- 
able, to  leave  the  autoclave  without  observation  during  sterilization, 
since  there  are  many  chances  for  mishaps ;  nevertheless,  if  the 
safety  valve  is  set  for  a  given  pressure,  steam  will,  of  course,  be 
blown  off  at  about  the  temperature  desired.  This  blowing  off  of 
steam  is  a  good  signal  for  cutting  off  a  part  of  the  gas  supply,  as 
the  rapid  escape  of  steam  not  only  results  in  exhaustion  of  the  small 
reservoir,  but  often  dislocates  the  cotton  plugs.  When  the  time 
for  sterilization  has  elapsed,  the  gas  is  turned  off ;  but  the  steam 
vent  should  be  only  gradually  opened  as  the  pressure  falls  to  100°  C., 
else  the  medium  may  boil  over  and  the  plugs  will  be  blown  out  of 
the  vessels.  If  steam  is  used  instead  of  a  gas  burner,  a  complicated 
set  of  stop-cocks  will  be  required,  or  will  at  least  be  advantageous, 
to  regulate  the  inlet  and  exit  of  the  steam. 

Hot  air  sterilization.  Implements,  glassware,  cotton,  sand,  and 
other  vessels  or  materials  used  in  culture  work,  which  may  not  be 
sterilized  by  steam  or  by  the  burner  flame  direct,  are  sterilized  in 
a  hot  air  sterilizer.  It  is  true  that  the  delicate  mycelium  and  spores 
of  many  fungi  are  often  injured  or  killed  by  drying  alone  ;  yet,  on 
the  other  hand,  the  spores  and  mycelium  of  many  fungi  are  ex- 
tremely resistant  to  desiccation  and  to  a  high  degree  of  dry  heat. 
By  long  practice  it  has  been  ascertained  that  it  is  not  safe  to  attempt 
to  sterilize  vessels  in  a  dry  oven  at  less  than  1 50°  C.  for  one  hour, 
or  at  a  slightly  lower  temperature  with  protracted  sterilization.  Test 
tubes  or  flasks  plugged  with  cotton,  or  Petri  dishes  wrapped  with 
paper,  cannot  well  be  exposed  to  a  much  higher  temperature. 
Glassware  may  safely  be  exposed  to  a  temperature  of  170°  C.,  or 
higher.  The  best  form  of  hot  air  sterilizer  is  the  Lautenschlager, 
Fig.  3,  yet  a  simple  and  inexpensive  oven  will  suffice. 

Sterilization  of  soil.  In  all  inoculation  work  where  there  is 
danger  of  contamination  from  the  soil,  and  particularly  in  the  study 
of  root  and  stem  diseases,  experiments  with  damping-off  fungi,  and 
the  like,  it  is  necessary  to  use  sterile  soil  and  sterile  pots.  The 
pots  may  be  prepared  with  soil  as  for  the  growing  of  any  plants, 
well  watered,  and  then  sterilized  a  few  at  a  time  in  any  steam  ster- 
ilizer or  autoclave.  In  the  former  they  should  be  sterilized  at  least 
two  or  three  hours  after  the  temperature  has  reached  100°  C.,  and 


22  CULTURE  METHODS  AND  TECHNIQUE 

this  should  be  repeated  if  possible  the  next  day.  This  method  is 
available  when  there  is  only  a  small  number  of  pots  to  be  handled. 
When,  however,  the  work  must  be  conducted  on  a  larger  scale 
an  effective  apparatus  is  the  Britton  soil  sterilizer.  Britton  has 
described 1  a  steam  sterilizer  for  soils  which  he  has  devised  for  use 
in  the  station  greenhouses.  This  apparatus  is  simple  and  seems  to 
be  wholly  practicable.  It  is  described  as  follows  : 

It  consists  of  a  square  box  made  of  heavy  galvanized  sheet-iron  connected 
with  the  steam-heating  system  in  the  potting  room  of  the  forcing-house  (or 
elsewhere  convenient).  This  box  is  cubical  in  form,  each  of  its  three  dimen- 
sions being  thirty  inches ;  six  inches  of  the  top  is  in  the  shape  of  a  removable 
cover.  Steam  enters  through  a  hole  in  the  center  of  one  side,  to  which  side  is 
soldered  a  coupling.  A  three-fourths  inch  pipe,  fitted  with  a  valve,  connects 
the  apparatus  with  the  steam-heating  system.  A  few  strips  of  wood  placed 
under  the  box  raise  it  a  half  inch  from  the  cement  floor  to  prevent  rusting. 
Inside  the  metal  box  are  similar  strips  upon  which  the  trays  rest.  Two  small 
holes  in  the  bottom  allow  the  condensed  water  to  escape. 

The  soil  is  placed  in  the  trays  which  are  made  of  wooden  frames  having 
bottoms  of  galvanized  wire  netting.  The  frames  are  made  of  strips  of  wood 
three  and  one-half  inches  wide  and  seven-eighths  of  an  inch  thick ;  after  fasten- 
ing the  netting,  a  half-inch  strip  is  nailed  on  to  hold  the  netting  firmly  and  to 
cover  its  jagged  edges.  The  dimensions'of  the  trays  in  inches  are  27  x  13  x  4 
over  all,  and  inside  are  25!  x  11^x3!  inches. 

The  wire  netting  has  six  meshes  to  the  inch.  Soil  is  spread  loosely  and 
evenly  in  the  trays  to  the  depth  of  about  three  inches  and  the  trays  packed 
inside  the  metal  box  in  cob-house  fashion.  .  .  . 

There  is  a  space  of  one  and  one-half  inches  all  around  the  trays  inside  the 
box,  and  a  space  of  an  inch  between  the  two  trays.  The  half-inch  strips  on  the 
bottom  edges  of  the  trays  allow  the  steam  to  enter  above  and  below  the  coil 
in  each  of  the  trays.  As  the  steam  comes  in  contact  with  the  soil,  both  above 
and  below  it,  much  less  time  is  required  to  heat  it  than  when  in  a  solid  mass. 
The  sterilizer  contains  fourteen  trays,  which,  when  filled  to  the  depth  of  three 
inches,  hold  6.9  cubic  feet  of  soil.  .  .  .  Steam  entering  through  a  three-fourths 
inch  pipe  at  a  pressure  of  five  pounds  per  square  inch,  heats  the  soil  to  the 
boiling  point  of  water  in  about  fifty  minutes  —  a  great  deal  depending,  of 
course,  on  the  density  of  the  soil,  as  a  loose  soil  heats  through  much  more 
rapidly  than  if  packed  closely.  The  box  is  not  steam  tight,  but  nearly  so  for  a 
low  pressure ;  considerable  expense  would  be  necessary  to  make  it  perfectly 
steam  tight  and  at  the  same  time  permit  of  convenience  in  opening  the  box. 

Soil  was  kept  in  the  apparatus  one  hour  for  the  purpose  of  killing  the  nem- 
atodes.  This  also  doubtless  destroyed  many  fungous  .germs,  but  where  absolute 

1  Britton  W.  E.  A  Steam  Sterilizer  for  Soils.  Conn.  (New  Haven)  Agl.  Exp. 
Sta.  Report  (1897):  310-312. 


ISOLATION  AND  PURE-CULTURE  METHODS         23 

sterility  from  bacteria  and  fungi  is  desired  it  would  be  necessary  to  steam  the 
soil  for  a  much  longer  time.  The  steamed  soil  is  also  almost  wholly  free  from 
live  seeds  of  weeds  while  the  untreated  soil  was  considerably  infested  with  vari- 
ous common  weeds. 

A  sterilizer  may  be  arranged  more  or  less  after  this  pattern,  but 
with  particular  reference  to  the  conditions  at  hand.  A  sterilizer  of 
this  type  may  also  be  used  for  pots  and  saucers  already  filled  with 
soil.  A  better  pressure  of  steam  may  be  secured,  of  course,  if  the 
sterilizer  is  directly  connected  with  the  boiler.  For  summer  work, 
moreover,  it  is  not  desirable  to  have  the  sterilizer  connected  with 
the  general  heating  system. 

Soil  sterilized  by  dry  heat  requires  a  very  high  temperature,  and 
is  unquestionably  somewhat  injured  in  the  process.  On  the  other 
hand,  it  must  be  remembered  that  soil  which  has  been  steam-ster- 
ilized encourages  upon  reinfection  the  growth  of  such  saprophytic 
organisms  as  Mucor  and  Penicillium,  and  possibly  such  hemisapro- 
phytes  as  Rhizoctonia  and  other  fungi  causing  root  diseases.  Care 
must  be  taken,  therefore,  not  to  permit  these  organisms  to  get  a 
start  in  the  soil  before  normal  bacterial  action  has  begun. 

IV.    PREPARATION  OF  CULTURE  MEDIA 
LIQUID  MEDIA 

Except  in  investigations  where  a  medium  of  known  composition 
is  required,  or  in  drop  cultures  and  the  like,  liquid  media  are  less 
used  for  cultural  purposes  with  the  fungi  than  with  the  bacteria. 
In  many  physiological  studies,  however,  such  media  are  desirable 
or  indispensable,  and  as  a  rule  these  liquid  media  form  the  nutrient 
bases  for  the  making  of  most  of  the  gelatinous  solid  media  employed 
in  mycological  work. 

Plant  decoctions  are  undoubtedly  of  the  first  value  for  work 
with  the  fungi,  and  with  these  organisms  they  may  entirely  replace 
bouillon,  considered  so  essential  in  the  culture  of  bacteria.  Some 
of  the  most  nutritious  and  convenient  plant  decoctions  may  be  made 
from  the  sugar  beet,  white  potato,  carrot,  pods  and  stems  of  bean, 
or  vetch,  prunes,  apples,  celery,  and  various  other  plants  or  plant 
products.  In  order  to  secure  more  or  less  uniformity  in  the  com- 
position of  these  decoctions,  for  every  1000  cc,  of  water  used  it 


24  CULTURE  METHODS  AND  TECHNIQUE 

has  been  my  practice  to  require  50  grams  dry  weight  of  the  plant 
product.  Accordingly,  from  a  mean  of  several  analyses  brought 
together,  it  would  require  about  490  grams  of  beet  root,  400  grams 
of  bean  stems  or  of  string  beans,  1 20  grams  of  dried  prunes,  and 
about  390  grams  of  the  fresh  potato. 

The  plant  product  is  washed,  and,  if  desirable,  pared,  cut  up 
finely,  or  thinly  sliced,  and  then  the  necessary  water  is  added.  It 
is  next  boiled  in  the  steam  sterilizer  for  about  two  hours,  or  in  the 
autoclave  at  1 1 5°  C.  for  twenty  minutes.  If  necessary  to  boil  over  a 
steam  bath,  a  flask  plugged  loosely  with  cotton,  or  a  small-mouthed 
agate  pitcher  covered  with  flannel,  should  contain  the  material,  so 
that  a  minimum  of  evaporation  will  occur.  The  clear  liquid  is  filtered 
off  through  several  thicknesses  of  filter  paper  into  a  sterile  flask, 
when  it  may  be  immediately  used  in  making  solid  media,  or  ster- 
ilized as  usual  for  preservation.  Where  it  is  particularly  desired 
to  obtain  the  clearest  decoction  possible,  the  liquid  may  be  cooled 
to  about  60°  C.  under  the  tap,  or  by  pouring  from  one  vessel  to 
another,  and  then  the  white  of  an  egg  may  be  added.  The  decoc- 
tion is  again  boiled  for  an  hour  in  the  sterilizer,  or  about  fifteen 
minutes  in  the  autoclave  ;  and  the  clear  liquid  finally  filtered  away 
from  the  coagulated  albumen  and  sediment. 

It  will  often  be  necessary,  or  well,  to  make  decoctions  of  various 
other  plants,  particularly  of  fleshy -fungi,  of  the  host  plants  upon 
which  certain  fungi  grow,  etc.  Such  decoctions  may  be  particularly 
desirable  in  physiological  work. 

Manure  decoctions  of  any  kind  are  particularly  serviceable  in  the 
study  of  many  saprophytic  organisms,  but  in  pathological  work 
these  liquids  are  no  more  valuable  than  any  of  the  plant  decoctions. 
Special  emphasis  might  be  laid  upon  prune  juice,  or  prune  decoc- 
tion, especially  when  the  fungus  is  one  which  may  inhabit  saccha- 
rine fruits,  berries,  etc. 

It  will  be  readily  suggested  to  the  student  that  plant  products 
of  various  kinds  may  be  roughly  grouped  into  such  as  are  rich  in 
albumens,  starches,  sugars,  etc.,  and  these  products  will  be  selected 
and  employed  in  accordance  with  such  indications  with  respect  to 
the  needs  of  the  fungus  as  are  available. 

Bouillon,  the  chief  fluid  medium  used  for  the  bacteria,  is  an 
extract  of  beef,  practically  a  beef  tea,  to  which  peptone  is  added. 


ISOLATION  AND  PURE-CULTURE  METHODS         25 

It  is  usually  made  directly  from  lean  beef,  and  is  an  infusion  of 
the  beef  in  twice  its  weight  of  water.  To  prepare  it,  500  grams  of 
lean  meat,  as  free  as  possible  from  fat,  are  chopped  or  ground 
finely,  and  to  this  is  added  1000  cc.  of  distilled  water.  It  is  then 
placed  in  a  cool  place  for  twelve  to  fifteen  hours,  and  occasionally 
stirred,  if  possible  ;  or  it  may  be  placed  in  a  water  bath  at  65°  C. 
and  frequently  stirred  for  a  period  of  about  one  hour.  By  the  latter 
method  the  bouillon  is  said  to  contain  some  less  desirable  substances, 
but  it  will  often  be  found  the  more  desirable  process  for  students 
who  cannot  be  at  the  laboratory  regularly.  All  of  the  juice  possible 
should  be  squeezed  out  of  -the  meat,  and  a  hand  press  is  frequently 
used  by  bacteriologists  to  accomplish  this  more  effectively.  The 
red  liquor  filtered  off  through  cheese  cloth  is  made  up  to  one  liter 
with  water,  and  then  to  it  is  added  I  o  grams  of  peptone  and  5  grams 
of  sodium  chloride.  It  is  then  heated  in  the  steam  sterilizer  for 
one  hour,  or  in  the  autoclave  fifteen  minutes,  when  a  clear  liquid 
with  a  well-differentiated  coagulum  is  to  be  seen.  This  is  filtered 
readily  through  filter  paper.  The  bouillon  will  now  be  slightly  acid 
and  should  be  neutralized  or  given  the  desired  reaction  with  sodium 
hydrate  (see  page  33).  For  ordinary  purposes  with  fungi  it  may 
be  enough  to  use  the  litmus  paper  test,  but  special  methods  of 
neutralization  are  essential  in  the  most  careful  work  either  with 
fungi  or  bacteria.  These  must  be  adhered  to  for  accurate  physio- 
logical work,  or  for  furnishing  descriptions  of  the  fungus  on  specified 
media.  If  the  bouillon  is  not  perfectly  clear,  an  egg  also  may  be 
used  as  with  the  plant  decoctions,  to  effect  clarification.  The  medium 
is  next  sterilized  and  preserved.  Prepared  meat  extracts  are  used 
by  some  in  making  bouillon. 

Milk  and  litmus  milk  are  only  important  with  the  bacteria. 
Fresh  milk  alone  should  be  employed,  and  from  this  the  cream 
should  be  removed  either  by  the  centrifuge  or  by  standing.  Litmus 
milk  is  made  by  the  addition  of  2  cc.  of  a  saturated  solution  of  blue 
litmus  to  each  100  cc.  of  milk.  This  is  extremely  sensitive  to  the 
development  of  alkalis  or  acids  during  the  growth  of  organisms. 

Synthetic  liquid  media,  as  they  are  termed,  that  is,  media  pre- 
pared by  the  use  of  salts,  carbohydrates  and  other  substances  of 
known  composition  are  more  extensively  used  in  physiological  work. 
There  the  specific  purpose  of  the  experiment  should  be  depended 


26  CULTURE  METHODS  AND  TECHNIQUE 

upon  to  determine  the  composition.  These  media  are,  however, 
important  in  all  culture  work.  The  following  solution  has  been  in 
such  common  use  as  to  be  generally  designated  a  standard  nutrient 
solution  : 

Ammonium  nitrate ,     .  i.o    gram 

Dihydrogen  potassium  phosphate .5    gram 

Magnesium  sulfate .25  gram 

Iron  chloride     . ' .  trace 

Cane  sugar 5.0    grams 

Water 100  cc. 

With  some  fungi  the  addition  of  a  small  quantity  of  sodium  chloride 
is  advantageous. 

Among  the  many  other  culture  fluids  which  have  been  used, 
one  of  the  most  important  available  alike  for  fungi  and  bacteria, 
although  not  ideally  constituted,  is  Uschinsky's  solution,  made  of  : 

Ammonium  lactate 6-7     grams 

Sodium  asparaginate 3-4     grams 

Potassium  hydrogen  phosphate 2-2.5  grams 

Magnesium  sulfate 0.3-0.4  grams 

Sodium  chloride 5-7     grams 

Calcium  chloride o.i  gram 

Glycerin ,     ....'_..'.     .     .  30-40  grams 

Distilled  water .' 1000  cc. 

Experience  in  culture  work  will  promptly  demonstrate  that  the 
concentrations  of  the  above  solutions  are  to  be  regarded  as  impor- 
tant because  they  establish  standards.  In  special  cases,  however, 
it  may  be  desirable  to  increase  considerably  the  amount  of  carbo- 
hydrate, and  this,  in  turn,  may  render  desirable  further  changes. 

SOLID  MEDIA 

Nutrient  agar  agar.  Agar,  or  agar  agar,  is  a  substance  some- 
what of  the  nature  of  gelatin.  It  is,  in  fact,  a  kind  of  gelatin,  or 
glutinous  substance,  made  from  certain  seaweeds,  especially  species 
of  Gelidium  (Fig.  6)  or  Gloiopeltis,  which  grow  abundantly  on  the 
coasts  of  Japan  and  China.  The  commercial  article  is  usually  ob- 
tained in  the  form  of  shred-like  strips,  or  as  a  powder.  Agar  has 
this  advantage  over  gelatin,  namely,  that  at  a  suitable  strength  it 
will  remain  solid  up  to  a  temperature  of  at  least  95°  C. ,  and  it 


ISOLATION  AND  PURE-CULTURE  METHODS         27 

very  seldom  becomes  liquefied  by  the  action  of  growing  organisms. 
Nutrient  agar  agar  consists  of  some  nutrient  "base,"  like  sugar 
beet  or  prune  decoction,  bouillon,  etc.,  to  which  is  added,  for  pur- 
poses of  solidification,  1 1  to  1 5  grams  of  the  commercial  agar  agar 
per  liter.  The  nutrient  base,  whether  plant  decoction  or  bouillon, 
may  be  made  as  already  indicated.  There  are  then  several  methods 
of  procedure  for  making  the  agar.  (i)  When  an  autoclave  is  at 
hand,  12  grams  of  the  agar  are  merely  cut  up  finely  into  a  liter 
of  the  desired  decoction  and  this  is  placed  in  the  autoclave  and 
steamed  at  from  1 10°  to  1 1 5°  C.  In  thirty  minutes  the  agar  will  be 


FIG.  6.   GELIDIUM  CORNEUM  LAM.,  FURNISHING  AGAR  AGAR 
(After  Erw.  F.  Smith) 

dissolved.  It  is  then  neutralized,  or  brought  to  the  desired  reaction ; 
and  if  not  clear,  the  white  of  an  egg  may  be  added,  as  usual,  when 
a  second  similar  or  shorter  steaming  is  necessary.  (2)  This  same 
method  may  be  used  with  the  steam  sterilizer,  except  that  it  may 
require  from  one  to  two  hours  for  the  complete  solution  of  the 
agar.  Some  grades  of  agar  dissolve  very  slowly  by  this  method, 
and  it  is  often  recommended  in  such  a  case  to  soak  the  agar  pre- 
viously twelve  to  eighteen  hours  in  water  containing  sodium  chlo- 
ride. (3)  Many  find  it  more  convenient  to  put  the  agar  into  an 
agate  iron  cup,  add  about  200  cc.  of  distilled  water  and  boil  directly 
over  a  flame,  stirring  constantly,  until  the  agar  is  thoroughly  dis- 
solved. This  is  then  added  to  the  decoction  to  be  used.  This  last 


28  CULTURE  METHODS  AND  TECHNIQUE 

method  requires  more  of  the  personal  attention  of  the  operator,  but 
it  insures  successful  solution  of  the  agar.  The  medium  may  be 
then  cleared  in  the  usual  manner. 

In  making  nutrient  agar,  a  chief  difficulty  for  the  beginner  has 
been  with  relation  to  filtration,  which  is  necessary  in  order  that  a 
clear  product  may  be  obtained  in  which  the  development  of  micro- 
colonies  may  be  carefully  followed.  If  the  agar  is  thoroughly  dis- 
solved, it  niters  with  comparative  ease  ;  whereas,  if  partly  dissolved, 
filtration  is  next  to  impossible.  In  any  case  a  grooved  or  ridged 
filter,  good  filter  paper  wet  with  hot  water  immediately  before  using, 
and  well-dissolved  agar  direct  from  the  pan,  steamer,  or  autoclave 
are  the  requirements.  Nevertheless,  in  case  of  difficulty,  the  filter 
stand  with  funnel  and  flask  may  be  placed  in  the  sterilizer  or  auto- 
clave to  be  kept  thoroughly  hot  during  the  process.  Again,- a  side- 
neck  filter  flask  may  be  used  so  that  connection  with  a  filter  pump 
attached  to  the  tap  may  be  secured.  In  the  latter  case  porcelain 
supports  and  cotton  may  be  substituted  for  filter  paper. 

After  filtration  the  agar  may  be  poured  into  flasks  or  test  tubes 
(usually  about  8  cc.  per  tube,  when  used  for  isolation  cultures), 
subsequently  sterilized  and  stored. 

A  synthetic  liquid  medium  may  be  used  as  a  nutrient  base  with 
agar.  The  standard  salt  solution  previously  mentioned  and  many 
others  are  serviceable ;  however,  since  agar  is  a  medium  the  com- 
position of  which  is  complex,  it  is  often  too  "  impure  "  as  to  known 
qualities  for  certain  physiological  studies.  Long  washing  is  of  value, 
but  this  may  not  remove  all  materials  furnishing  food  substances. 
A  few  drops  of  hydrochloric  acid  in  the  water  will  also  materially 
improve  the  purity  of  the  agar,  but  it  may  injure  or  entirely  destroy 
the  solidifying  properties.  In  most  instances  it  is  best  to  substitute 
for  the  agar  Winogradsky's  silicate  jelly,  or  resort  to  cultures  on 
tightly  folded  bars  of  filter  paper  or  some  other  pure  substance. 
Glycerin  agar  is  particularly  serviceable  in  culturing  slow-growing 
fungi.  It  is  made  by  the  addition  of  5  per  cent  glycerin  to  the 
prepared  medium. 

A  stiff  agar,  made  by  using  from  twenty  to  thirty  grams  of  agar 
for  each  liter  of  solution,  is  desirable  when  cultures  are  to  be  trans- 
ported. It  is  also  valuable,  employed  in  large  flask  cultures,  in 
order  to  obtain  the  fruiting  stages  of  many  fungi. 


ISOLATION  AND  PURE-CULTURE  METHODS 


29 


Nutrient  gelatin  is  employed  extensively  in  the  cultivation  of 
bacteria,  but  seldom  with  the  fungi.  It  is  made  by  adding  100 
grams  of  gelatin  to  each  1000  cc.  of  bouillon.  In  the  preparation 
of  this  medium  one  must  use  as  little  heat  as  possible.  It  dissolves 
readily  in  hot  bouillon,  and 
filters  much  more  quickly 
than  agar.  The  congealing 
properties  of  gelatin  are  de- 
stroyed by  a  long  exposure  to 
a  greater  temperature  than 
1 00°  C .,  so  that  if  the  autoclave 
is  employed,  then  the  gelatin 
should  be  cooled  promptly. 
When  sterilized,  the  periods 
of  steaming  should  not  exceed  FIG.  7.  DOUBLE-WALLED  METAL  Box  FOR 

ten  or  fifteen  minutes.    Gela-    STORAGE   OF   GELATIN   CULTURES;    CON- 

NECTED  WITH  WATER  SUPPLY.  ( After  Novy) 
tin  melts  at  a  temperature 

above  35°  C.  and  often  lower,  so  that  it  must  be  stored  in  a  cool 
place ;  and  the  cold  water  box  of  Novy  (Fig.  7)  may  be  used  to  afford 
such  a  low  temperature  when  the  refrigerator  is  unsatisfactory. 

Starch  jelly  should  become  an  important  nutrient  medium.  It 
can  be  obtained  fairly  pure,  and  in  connection  with  synthetic  salt 
solutions  it  is  valuable  for  slanting  tubes.  Commercial  starches 
generally  contain  resistant  spore-forming  organisms,  and  it  is  desir- 
able to  shake  up  the  starch  in  a  flask  with  95  per  cent  alcohol  for 
one  hour  and  dry  rapidly  on  filter  paper  before  using.  A  10  per 
cent  mixture  in  the  salt  solution  selected  should  be  made.  Rub  this 
up  well  before  heating,  and  sterilize,  if  possible  at  from  90°  to  93° 
C.  on  successive  days. 

Vegetable  products.  Cylinders  or  slices  of  vegetables,  such  as 
the  sugar  beet  or  potato,  or  even  young  stems  or  pods  of  bean, 
prunes,  squash,  corn  meal,  etc.,  prove  excellent  media  of  different 
types,  most  suitable  for  work  with  the  fungi.  The  sugar  beet  is  an 
excellent  general  medium,  rich  in  cane  sugar.  It  is  quite  generally 
obtainable  during  the  autumn,  and  laboratories  may  then.be  pro- 
vided with  a  supply  which  will  keep  in  a  cellar  over  winter.  The 
potato  is  always  available  and  offers  an  excellent  starchy  medium. 
The  stems  or  young  pods  of  bean  are  rich  in  nitrogenous  material , 


30  CULTURE  METHODS  AND  TECHNIQUE 

but  in  the  preparation  of  these  more  care  is  necessary  for  the  pre- 
vention of  bacterial  contamination.  This  is  one  of  the  most  nutri- 
tious culture  media  known  for  fungi  in  general.  String  beans  may 
be  obtained  on  the  market  at  almost  any  season.  Celery  leaf  stalks 
are  a  medium  rich  in  nitrates  and  desirable  for  some  organisms. 
All  of  these  highly  nutritious  media  are  excellent  for  securing  the 
vegetative  growth  of  an  organism,  but  it  is  very  often  the  case 
that  with  such  media  fruiting  stages  are  not  obtainable.  I  have 
almost  invariably  obtained  better  fruiting  stages  by  using  ordinary 
corn  meal,  or  maize  meal.  This  can  be  prepared  to  advantage  in 
small  flasks.  The  flask  is  filled  with  meal  to  a  depth  of  about  two 
thirds  of  an  inch.  This  is  then  wet  with  water,  hot  water  being 
preferable,  as  cold  water  does  not  wet  it  so  readily ;  and  enough 
water  is  added  to  make  the  meal  quite  soft,  since  considerable  water 
will  be  absorbed  during  sterilization.  Cylinders  or  plugs  of  various 
root  crops,  or  stems  of  plants,  dead  wood,  and  various  other  products, 
may  serve  special  purposes. 

In  preparing  the  cylinders  of  root  crops,  the  roots  should  be 
thoroughly  washed  and  pared,  and  then  cut  into  pieces  of  desired 
size.  If  used  in  a  test  tube,  a  scoop  which  cuts  out  a  cylindrical 
piece  will  be  found  convenient.  These  cylindrical  plugs,  say  three 
inches  long,  are  then  cut  diagonally.  Ordinarily  a  piece  is  placed  in 
a  test  tube  of  1 2  —  1 5  x  1 50  —  180  mm.,  and  then  ^  to  I  inch  of 
water  is  added.  More  desirable  for  many  purposes,  and  particularly 
for  transportation,  is  to  put  in  each  tube  half  an  inch  or  so  of  satu- 
rated absorbent  cotton,  and  within  this  rests  the  end  of  the  nutrient 
substance,  which  is  thus  firmly  held  in  place.  The  latter  method 
avoids  all  fluids  in  the  cultures,  and  the  tubes  may  be  inclined  or 
placed  upright  afterwards,  as  convenient.  In  somewhat  the  same 
way  wads  of  absorbent  cotton  or  of  filter  paper  may  be  placed  in 
the  tubes,  and  these  wads  then  moistened  or  wet  with  any  nutrient 
solutions  desired,  and  subsequently  sterilized.  Closely  folded  pieces 
of  filter  paper  may  be  used  in  this  way  with  solutions  of  known  com- 
position for  very  accurate  work  in  nutrition ;  and  in  such  cases  a 
supply  of  the  liquid  may  also  be  placed  in  the  tube  so  that  the 
culture  may  not  dry  out  for  a  considerable  period. 

It  is  often  desirable,  and  indispensable  for  the  best  growth,  to 
use  in  connection  with  a  culture  liquid  of  known  composition  some 


ISOLATION  AND  PURE-CULTURE  METHODS         31 

solid  substratum,  serving  principally,  perhaps,  as  a  means  of  aeration. 
Wads  of  pure  filter  paper,  or  elder  pith  which  has  been  carefully 
purified,  are  both  serviceable. 

Certain  parasitic,  fleshy,  or  bracket  fungi  may  be  grown  to  advan- 
tage upon  dead  or  normal  wood.  With  a  proper  regulation  of  the 
moisture  content  of  the  culture  chamber  fruiting  is  often  readily 
induced  upon  such  media  when  other  substrata  fail. 

Silicate  jelly.  Silicate  jelly  as  a  substitute  for  gelatin  and  agar 
was  introduced  primarily  to  overcome  the  difficulties  experienced 
in  isolating  certain  organisms  in  the  cultivation  of  which  it  is  de- 
sirable to  avoid  organic  media.  There  is,  however,  a  much  wider 
use  for  this  preparation.  As  finer  methods  are  developed  it  be- 
comes more  and  more  desirable  to  employ  synthesized  media  for 
a  variety  of  purposes.  At  best  gelatin  and  agar  are  of  uncertain 
composition,  and  when,  for  example,  one  wishes  to  determine 
accurately  the  value  of  nutrient  substances  for  an  organism  re- 
quiring solid  media,  silicate  jelly  is  most  serviceable.  This  material 
is  not  difficult  to  prepare  when  precautions  are  taken,  and  the 
writer  has  found  it  practicable  in  connection  with  any  mineral  or 
organic  nutrients  tested. 

The  following  materials  and  special  apparatus  will  be  required 
for  500  cc.  of  the  silicate  jelly. 

a.  i  Baume  hydrometer  for  liquids  heavier  than  water. 

b.  200  cc.  HC1  (sp.  g.  1.10°  Baume). 

c.  200  cc.  sodium  silicate  (sp.  g.  1.09°). 

d.  collodion  sacks  for  dialyzing. 

e.  100  cc.  nutrient  salt  solution  five  times  desired  strength. 
Stock  solutions  of  b  and  c  may  be  kept  on  hand,  also  of  e,  if 

the  same  nutrients  are  to  be  employed  in  many  experiments. 
Strong  hydrochloric  acid  is  diluted  with  pure  distilled  water  to 
test  1.10°  Baume  at  15°  C. 

Sodium  silicate,  water  glass,  is  obtainable  at  a  specific  gravity 
of  about  1.38  to  1.42.  Distilled  water  may  be  added  to  this  slowly 
until  the  hydrometer  registers  1.09°  B.  It  will  usually  require 
about  seven  or  eight  times  as  much  distilled  water  as  silicate  to 
give  the  specific  gravity  desired.  When  required  the  standardized 
silicate  is  then  added  cautiously  (dropping  rapidly)  to  the  acid,  con- 
stantly stirring. 


32  CULTURE  METHODS  AND  TECHNIQUE 

Collodion  for  the  dialyzing  sacks  is  prepared  by  dissolving  five 
grams  of  guncotton  in  100  cc.  of  a  solvent  consisting  of  equal 
parts  of  absolute  alcohol  and  sulfuric  ether.  The  sacks  are  prefer- 
ably prepared  by  the  test  tube  method,  and  convenient  tubes  will 
measure  about  30  by  200  mm.,  with  lip.  The  tubes  must  be  thor- 
oughly cleaned  (a  final  rinsing  with  ether  being  desirable)  and 
dried.  The  tube  is  held  in  a  slanting  position  and  gradually  re- 
volved as  about  50  cc.  of  the  collodion  is  slowly  poured  in,  and 
thus  an  even  roll,  or  coating  throughout,  with  no  bubbles,  should 
be  effected.  A  second  coating  is  obtained  by  similarly  revolving 
the  tube  as  the  surplus  collodion  is  poured  out.  The  tubes  are 
then  supported  upright,  mouth  downward,  and  the  drip  at  the  lip 
removed.  They  should  then  be  dried  rapidly  in  a  draft  at  a 
window  or  preferably  under  an  electric  fan,  or  by  exhaust,  con- 
stantly revolving  each  tube  meanwhile  to  maintain  even  distribution 
of  the  collodion.  When  dry,  first  free  the  edge  of  the  collodion 
from  the  tube  with  a  scalpel  and  then  immerse  the  tube  in  a  vessel 
of  water  so  that  as  the  sack  is  made  free  water  will  pass  in  between 
the  collodion  film  and  the  glass,  and  thus  the  removal  of  the  film 
may  be  readily  effected. 

The  silicate  mixture  is  put  in  these  tubes  and  they  are  tied 
securely  with  a  rubber  cord  and  suspended  in  water  over  night. 
Running  tap  water  may  be  commonly  employed,  but  for  more 
accurate  work  it  will  be  necessary  to  use  changes  of  distilled  water. 
The  dialyzed  liquid  should  react  neutral  to  litmus  and  should  show 
only  a  trace  of  chlorides  with  silver  nitrate. 

The  nutrient  solution  employed  may  be  that  mentioned  on  page 
26,  except  that  the  concentration  is  five  times  as  strong,  as  pre- 
viously indicated.'  It  is  now  necessary  to  boil  both  the  silicate 
preparation  and  the  nutrient  solution  a  few  minutes  to  remove  air. 
Then  cool  down  to  room  temperature,  mix  and  stir,  and  put  into 
the  separatory  funnel  to  facilitate  pipetting  into  tubes  or  other 
vessels  to  be  employed  in  the  work.  The  silicate  in  the  desired 
vessels  is  then  autoclaved  for  about  fifteen  minutes.  This  should 
insure  thorough  solidification.  Slanting  tubes  may  also  be  pre- 
pared. It  may  be  necessary  for  the  operator  to  vary  the  concen- 
tration of  the  salts,  or  to  experiment  with  small  quantities  when 
using  unusual  proportions  of  mineral  salts. 


ISOLATION  AND  PURE-CU 

NEUTRALIZATION  OF/t 

Neutralization,  or  properly  titrltoef^  of  most  culture  #&Jia  is 
required.  It  is  required  in  order  that  definite  standards  may  be 
maintained.  In  fact,  titration  is  superfluous  only  in  rough  work. 
In  general,  the  degree  of  alkalinity  or  acidity  of  the  medium  may 
affect  some  of  the  characteristics  of  organisms,  and,  therefore,  a 
description  of  any  organism  should  be  made  either  at  a  fixed 
standard  of  alkalinity  or  acidity,  or  it  should  at  least  be  possible 
to  reproduce  exactly  the  reaction  of  the  medium  employed.  The 
colonies  of  Bacillus  prodigiosus  and  other  pigment-forming  bac- 
teria are  less  brilliantly  colored  when  the  media  are  distinctly  acid. 
To  slight  differences  of  reaction  in  the  substratum  fungi  ordinarily 
show  no  marked  cultural  variations  ;  yet  to  greater  differences  they 
may  respond  by  variations  in  color,  modifications  of  colony  form, 
amount  or  character  of  fruiting,  etc. 

Most  culture  media  are  acid,  and  sodium  carbonate  was  formerly 
employed  in  neutralization.  From  this,  however,  carbonic  acid  is 
liberated,  and  litmus  is  temporarily  reddened,  so  that  potassium 
hydrate  or  sodium  hydrate  is  preferable.  Moreover,  in  this  titration 
work  phenolphthalein,  a  reliable  indicator,  has  been  adopted.  It  is 
more  desirable  than  litmus,  rosolic  acid,  or  other  indicators.  Litmus 
may  be  used  for  rough  work,  but  it  is  less  sensitive  to  certain  acids 
and  too  variable.  In  peptone,  gelatin,  and  other  organic  substances 
there  are  bodies  which  are  amphoteric,  that  is,  which  possess 
both  basic  and  acid  properties,  the  latter  predominating.  Phenol- 
phthalein is  particularly  serviceable  with  respect  to  those  substances. 
Litmus  fails  to  detect  such  weak  acids  ;  again,  litmus  reacts  alkaline 
to  the  dibasic  phosphates,  while  phenolphthalein.  reacts  neutral. 

In  titration,  the  following  solutions  are  desirable  :  \  per  cent 
phenolphthalein  in  50  per  cent  alcohol,  as  indicator ;  ^  normal 
caustic  alkali  (preferably  sodium  hydrate)  for  the  titration  ;  and 
a  normal  solution  of  the  caustic  alkali  for  actual  neutralization  of 
the  medium.1 

1  For  practical  purposes,  a  normal  solution  of  sodium  hydrate  may  be  prepared 
by  dissolving  4.5  grams  of  c.p.,  fresh  NaHO  in  somewhat  less  than  100  cc.  of 
distilled  water,  and  after  it  is  dissolved  make  up  with  water  to  exactly  100  cc. 
(roughly,  this  amount  makes  due  allowance  for  the  water  and  impurities  in  fresh 
NaHO). 


34  CULTURE  METHODS  AND  TECHNIQUE 

Fuller's  procedure  modified  may  then  be  a  guide  ;  this  is  as 
follows:  (i)  Measure  by  a  volumetric  pipette  or  burette  5  cc.  of 
the  culture  medium,  and  dilute  it  with  distilled  water  to  50  cc. 
(2)  Boil  for  three  minutes  in  a  porcelain  dish.  (3)  Add  I  cc.  of  the 
stock  solution  of  the  indicator,  phenolphthalein,  and  titrate  by  add- 
ing the  J0  per  cent  caustic  alkali  from  a  burette.  Stir  constantly, 
and  a  permanent  faint  pink  coloration  will  indicate  the  first  appear- 
ance of  alkalinity.  Those  inexperienced  in  the  work  should  always 
take  two  or  even  three  samples  of  the  culture  liquid  and  compare 
results  as  to  the  amounts  of  alkali  employed.  The  data  are  then  at 
hand  for  neutralization  or  for  making  the  medium  correspond  to  a 
desired  reaction.  If  6  cc.  of  the  ^  normal  alkali,  for  example,  is 
required  to  bring  the  two  samples  to  the  point  of  neutralization, 
then  the  remaining  990  cc.,  assuming  that  we  employ  a  liter  of 
culture  medium,  would  require  practically  100  times  6  cc.,  or  600  cc. 
of  TTQ  normal,  which  is  equivalent  to  30  cc.  of  normal  alkali.  Ordi- 
narily, the  medium  is  not  neutralized,  but  is  left  acid  to  the  extent  of 
an  omission  of  10— 1 5  cc.  of  normal  alkali  per  liter.  In  the  example 
above,  therefore,  15  or  20  cc.  of  normal  alkali  would  be  added. 
A  control  titration  may  also  be  made. 

V.    PRESENT  METHOD  OF  ISOLATING  ORGANISMS 

In  making  cultures  with  a  view  of  isolating,  or  separating  out 
various  microscopic  organisms,  the  poured-plate  (Petri  dish)  method 
is  now  almost  exclusively  employed.  Such  cultures  may  be  called 
isolation  or  separation  cultures,  the  use  of  the  old  term  dilution 
culture  being  less  desirable. 

Materials  needed.  In  order  to  make  these  isolation  cultures,  one 
requires  nutrient  media  and  apparatus  more  or  less  as  follows  : 

Sterilized  Petri  dishes,  of  about  100  mm.  diameter ;  test  tubes 
containing  about  10  cc.  of  sterile  agar  agar ;  a  few  very  short  test 
tubes  without  agar ;  a  platinum  needle  ;  a  beaker,  or  tumbler,  with 
some  cotton  in  it,  to  hold  the  tubes  ;  a  thermometer ;  and  some 
boiling  water.  The  agar  in  the  tubes  is  melted,  either  in  the  steam 
sterilizer  or  in  an  open  casserole  of  boiling  water  with  cloth  or 
cotton  at  the  bottom.  In  ordinary  culture  work,  as  well  as  in  bac- 
teriological work,  three  tubes,  and  consequently  three  Petri  dishes, 
constitute  an  isolation  series.  Three  tubes  of  melted  agar  are 


ISOLATION  AND  PURE-CULTURE   METHODS 


35 


placed  in  the  beaker,  which  is  filled  with  water  at  from  4O°-42°  C. ; 
and  this  temperature,  which  is  above  the  point  of  solidification  of 
agar,  should  be  maintained  throughout  the  period  of  culture  by  the 
addition  of  hot  water  when  necessary. 

The  method.  In  making  the  cultures  the  procedure  may  be  as 
follows  :  Some  of  the  spores  or  bits  of  the  material  from  which 
cultures  are  desired  are  diffused  in  a  drop  of  sterile  water  placed 
in  one  of  the  short  test  tubes  (or  a  flamed  slide  will  suffice).  The 
three  tubes  in  the  beaker  are  denoted  i,  2,  and  3  respectively,  and 
may  be  so  marked  with  a  wax  pencil.  The  short  tube  containing 
the  spores  and  tube  No.  I  are  taken  between  the  thumb  and  index 


FIG.  8.   Two  DISHES  FROM  AN  ISOLATION  SERIES  OF  A  PARASITIC  FUNGUS 
(Photograph  by  Geo.  F.  Atkinson) 

finger  and  the  index  and  middle  fingers  respectively,  and  held 
almost  horizontal,  palm  upward,  the  plugs  having  been  previously 
removed  and  held  between  the  spaces  of  the  remaining  fingers. 
The  flamed  but  cold  platinum  needle,  provided  with  a  loop  at  the 
tip,  is  taken  in  the  right  hand,  dipped  into  the  drop  of  spores,  and 
then  into  the  agar  of  No.  I  and  mixed.  This  may  be  repeated 
several  times,  unless  the  spores  in  the  drop  are  very  numerous. 
No.  i  is  now  placed  in  the  former  position  of  the  short  tube,  and 
No.  2  in  the  place  of  No.  i.  The  process  is  repeated  with  this 
combination,  and,  finally,  with  Nos.  2  and  3  ;  the  contents  of  each 
tube  is  then  poured  into  a  corresponding  Petri  dish  upon  the  top 
of  which  number,  date,  and  any  description  desired  may  be  in- 
scribed with  the  wax  pencil. 


36  CULTURE  METHODS  AND  TECHNIQUE 

Frequently,  it  will  be  found  in  practice  that  in  making  cultures 
of  many  parasitic  fungi  so  few  spores  will  be  available  that  they 
may  be  inserted  directly  into  tube  No.  i,  and  it  will  be  necessary 
to  pour  a  few  drops  of  the  agar  from  No.  I  to  No.  2.  In  fact, 
No.  2  will  usually  give  a  very  good  isolation ;  and  then  No.  3  may 
be  used  as  a  No.  2,  to  which  is  added  a  drop  of  50  per  cent  lactic 
acid.  Fig.  8  shows  an  isolation  series  of  Glomerella  rufomaculans •, 
the  bitter  rot  fungus. 

Elimination  of  bacteria  in  isolating  fungi.  The  use  of  lactic  acid 
in  culture  media  is  an  important  aid  in  eliminating  certain  trouble- 
some bacteria.  In  general  it  may  be  well  to  prepare  some  tubes 
with  lactic  acid  in  about  the  amount  above  indicated,  practically  .5 
per  cent,  so  that  all  tubes  used  in  the  isolation  series  may  be  thus 
acidulated  without  danger  of  contamination.  Acidulated  media  are 
especially  valuable  when  separation  cultures  must  be  made  by  using 
hyphae  from  a  mixed  culture,  or  from  any  other  source  which  permits 
extraneous  organisms  to  come  in.  In  such  cases  the  mycelium 
should  be  washed  as  carefully  as  possible  in  distilled  water,  and  then 
on  being  placed  in  the  tubes  of  liquefied  agar,  the  tubes  should  be 
vigorously  shaken  before  the  contents  are  poured  into  the  Petri 
dishes.  If,  however,  there  is  nothing  to  indicate  the  relations  of 
a  fungus  to  acidity,  one  isolation  series  should  be  made  with 
neutral,  or  very  slightly  acidulated  agar. 

Colony  counting.  In  bacteriological  work,  and  sometimes  in 
purely  mycological  work,  it  is  desirable  to  make  accurate  count  of 
the  number  of  spores  or  cells  which  may  have  been  present  in  the 
material  from  which  the  culture  is  made.  Under  such  circumstances 
a  leveling  table  must  be  employed  in  making  the  poured  plates  or 
Petri  dish  isolation  cultures.  Plates  of  glass  or  other  devices,  such 
as  cardboard  charts,  especially  calibrated  for  counting  colonies  will 
also  be  necessary. 

Study  of  the  isolation  colony.  In  the  study  and  transference 
of  the  fungi  which  may  appear  in  isolation  cultures,  there  is  a 
rough  method  which  may  be  pursued,  and  there  is  a  careful  method 
which  must  be  followed  if  one  is  to  be  sure  that  the  life  history  of 
a  particular  fungus  has  been  accurately  traced.  In  the  first  place, 
one  may  wait  until  the  colonies  have  appeared,  and  perhaps  until 
growth  has  been  considerably  advanced.  Then,  if  isolation  is 


ISOLATION  AND  PURE-CULTURE  METHODS         37 

perfect,  the  species  may  be  more  or  less  readily  differentiated,  and 
with  a  sterile  needle  transfers  may  be  made  of  each  of  the  one  or 
more  promising  sorts  to  such  media  as  may  have  been  prepared 
for  the  purpose.  This  method  suffices,  of  course,  when  the  desire 
is  merely  to  get  cultures  of  different  fungi.  When,  however,  one 
wishes  to  get  the  product  of  a  certain  kind  of  spore,  it  is  absolutely 
essential  to  follow  the  germination  of  this  spore  in  the  Petri  dish, 
to  locate  germinating  spores  at  a  distance  from  any  other  organ- 
isms, and  then  to  mark  the  glass  and  observe  these  from  day  to  day 
or  to  directly  remove  these  isolated  spores  with  some  of  the  sur- 
rounding agar  by  means  of  a  sterile  needle,  or  scalpel  point,  to 
tubes  of  prepared  media.  In  the  latter  case  a  considerable  number 
of  such  cultures  should  be  made,  and  the  results  may  not  be  taken  as 
entirely  conclusive  unless  there  is  agreement  between  the  cultures 
thus  made.  When  the  fungus  is  one  possessing  characters  by  means 
of  which  it  may  be  readily  determined,  the  problem  is  not  difficult. 

Frequently  the  spores  which  are  to  be  located  are  so  small  that 
it  will  be  necessary  to  remove  the  cover  of  the  Petri  dish,  and  to 
examine  it  fearlessly  with  the  agar  surface  exposed.  If  carefully 
done,  the  contaminations  resulting  are  practically  negligible.  It 
will  be  necessary  to  use  an  objective  with  a  long  working  distance 
and  the  |-inch  or  ^-inch  is  preferable.  A  rough  examination, 
where  the  spores  are  large,  may  be  given  by  inverting  the  dish  and 
cover,  making  the  examination  from  the  bottom,  and  then  the 
location  of  spores  may  be  indicated  by  ink  marks. 

Establishing  pure  cultures:  subcultures.  The  process  of  trans- 
planting bacteria,  spores,  or  mycelial  masses  from  an  isolation  cul- 
ture to  sterile  tubes  of  prepared  media  is  properly  that  of  establishing 
pure  cultures.  Frequently  it  is  desirable  to  make  a  large  number 
of  such  subcultural  transplantings  to  be  used  as  the  stock  cultures 
from  which,  in  future,  any  necessary  series  of  experiments  may 
proceed. 

Under  ordinary  laboratory  conditions,  tube  cultures  may  begin  to 
dry  out  in  from  six  weeks  to  several  months,  and  must  therefore  be 
renewed  or  transferred.  This  consists  merely  in  inoculating  fresh 
tubes  from  the  old  cultures.  A  record  of  such  transfers  is,  for 
physiological  purposes  at  least,  important,  and  may  be  indicated  on 
the  label,  or  in  the  record  book. 


38  CULTURE  METHODS  AND  TECHNIQUE 

In  making  transfers  and  in  examining  any  tube  culture,  it  is 
well  to  flame  the  plug  lightly  before  removal,  otherwise  particles  of 
dust  from  the  surface  may  fall  into  the  tube  and  contaminate  it. 
The  flaming  should  be  momentary,  and  if  the  tube  is  turned  so 
that  the  plugged  end  is  distant  from  the 
operator,  it  will  be  easy  to  blow  out  the 
flame.  The  cork  should  be  removed  slowly 
so  that  there  may  be  no  rush  of  air  into  the 
tube,  thus  bringing  contaminating  dust  par- 
ticles. It  is  needless  to  say  that  wherever 
possible  tubes  should  be  held  horizontally, 
or  as  nearly  so  as  the  contents  will  permit. 
Storage  of  cultures.  In  general,  it  is  not 
well  to  store  tube  cultures  in  a  damp  place. 
If  moisture  is  constantly  in  contact  with  the 
glass,  or  extends  through  the  cotton  plug, 
bacteria  will  readily  enter  the  tubes.  Again, 
under  such  circumstances  fungous  spores 
may  also  germinate,  the  mycelium  may  grow 
through  the  plug,  and  fruit  on  the  lower  side  ; 
thus  spores  will  drop  into  and  contaminate 
the  culture.  When  the  plugs  become  wet 
during  sterilization,  particularly  those  clos- 
ing flasks  of  media,  the  flasks  should  be 
re-sterilized  after  the  plugs  are  dry,  or  after 
fresh  plugs  are  inserted.  When  placed  in 
storage,  a  paper  cone  may  be  placed  over  a 
few  tubes  or  a  crate,  or  under  some  circum- 
stances, particularly  where  it  is  desirable  also 
FIG.  9.  CULTURE  OF  PLEU-  to  prevent  rapid  evaporation,  one  may  em- 
ROTUS  OSTREATUS  JACQ.  ploy  the  rubber  caps  which  may  be  obtained 

rom  a  Tissue  Fragment)    for  ^  purpose<     A  refrigerator  is  desirable 

whenever  cultures  are  to  be  maintained  fresh  for  a  long  period. 
In  this  case  the  ice  chamber  should  have  no  connection  with  the 
storage  chambers.  Small  compartment  cases,  such  as  sectional 
bookcases,  are  very  serviceable  for  storing  cultures  away  from  the 
dust,  under  laboratory  conditions.  The  culture  room  (Fig.  14)  is 
cleaner  when  the  cultures  are  stored  elsewhere. 


ISOLATION  AND   PURE-CULTURE  METHODS 


39 


Sealing  cultures.  In  order  to  seal  the  tubes  permanently,  sealing 
wax  may  be  used  after  pushing  the  plug  in  somewhat  below  the 
level  of  the  glass.  Ordinary  beeswax  is  also  effective  if  a  little  ster- 
ile paraffin  is  first  poured  over  the  plug  and  permitted  to  harden. 
The  length  of  life,  of  a  culture 
may  sometimes  be  preserved  in 
this  way  for  several  years. 

If  the  cultures  are  placed  in  a 
damp  place,  as  in  a  closed  box  or 
case,  with  a  surface  of  water 
evaporating,  so  as  to  diminish  the 
loss  of  water  from  the  tubes  them- 
selves, it  would  be  well  to  wipe 
out  the  case  carefully  with  a  dis- 
infectant before  use.  Where  it  is 
desired  wholly  to  prevent  evapora- 
tion under  normal  conditions  of 
aeration  a  different  method  is  nec- 
essary. The  cultures  may  be  put 
into  a  clean  beaker  or  tin  vessel 
fitted  with  a  zinc  screen,  or  cross 
wired  with  copper,  serving  to  sep- 
arate the  tubes  from  contact  one 
with  another.  After  thoroughly 
flaming  the  corks  the  vessel  of 
tubes  may  be  placed  in  a  small 
dish  or  plate  of  water  containing  a 
little  potassium  dichromate  and 
the  whole  covered  with  a  clean 
bell  glass. 

Cultures  by  sporophore  frag- 
ments. In  his  studies  upon  Agar- 
icus  campestris  the  writer  ascer- 
tained that  fragments  of  the  inner  tissue  of  the  hymenophore  of 
this  fungus  placed  upon  a  sterile  nutrient  medium,  such  as  bean 
pods,  sterile  compost,  soil,  etc.,  would  readily  develop  a  vigorous 
mycelium.  In  order  to  secure  cultures  of  this  particular  species 
promptly,  it  was  necessary  (i)  to  use  proper  sterilization  and 


FIG.  10.    CULTURE  OF  POLYPORUS 

SULPHUREUS(R\J"LI..}  FR.,  A  SPECIES 

TOUGH   IN  TEXTURE.    (By  Tissue 
Fragment  Method) 


40  CULTURE  METHODS  AND  TECHNIQUE 

antiseptic  precautions  with  all  material  used  ;  (2)  to  take  fragments 
from  a  developing  (growing)  hymenophore  and  not  from  one  mature 
or  decaying  ;  and  (3)  to  employ  a  suitable  nutrient  medium.  Under 
such  conditions  growth  is  practically  invariable  (Figs.  9,  10),  unless 
bacteria  have  previously  gained  access  to  the  mushroom  or  the 
culture  accidentally  becomes  contaminated. 

This  method,  or  what  was  practically  the  same,  has  doubtless 
been  occasionally  resorted  to  much  earlier  for  obtaining  cultures  of 
a  few  fleshy  fungi,  though  practically  no  attention  has  been 
bestowed  upon  the  method.  The  method  is,  however,  capable  of 
being  used,  and  has  frequently  been  used,  in  securing  cultures  from 
sclerotial  stages,  and  the  writer  has  often  employed  it  in  obtaining 
cultures  of  such  stages  of  certain  Sclerotinias.  No  attempt,  how- 
ever, had  previously  been  made  to  determine  its  general  applica- 
bility. During  the  past  few  years  this  method  has  been  employed 
with  a  great  variety  of  fungi,  —  Discomycetes,  certain  Pyrenomy- 
cetes,  and  a  considerable  number  of  Basidiomycetes,  among  which 
were  forms  widely  different  as  to  relationship,  texture,  and  habitat. 
A  record  was  kept  of  the  trials  made  with  sixty-nine  species  of 
Basidiomycetes,  and  of  these,  forty  grew  promptly  on  the  media 
first  employed.  The  method  is  especially  serviceable  in  securing 
cultures  of  forest-tree  fungi  and  other  fleshy  or  woody  forms  the 
spores  of  which  may  germinate  only  with  great  difficulty. 


CHAPTER    II 

TECHNIQUE  OF  FIXING,  IMBEDDING,  AND  STAINING 

CHAMBERLAIN,  C.  J.    Methods  in  Plant  Histology.  (2d  ed.)  262  pp.  87 Jigs. 

1905. 

LEE,  A.  B.    Microtomist's  Vade  Mecum.    (6th  ed.)    538  pp.    1905. 
ZIMMERMAN,  A.    (Transl.  by  J.  E.   Humphrey.)    Botanical   Microtechnique. 

296  pp.    1893. 

I.    FIXING 

The  purpose  of  a  fixing  agent  is  to  kill  and  fix,  or  render  per- 
manent, the  structural  relations  of  the  cell  and  the  associations  of 
cells  in  tissues.  The  finer  protoplasmic  structures  are  readily  dis- 
organized and  lost  for  study,  if  not  carefully  fixed  by  special  agents. 
Moreover,  adequate  fixing  is  necessary  in  order  to  prepare  tissues 
to  show  properly  the  differential  effects  which  may  be  gained  by 
staining.  It  is  well,  therefore,  to  fix  by  one  or  more  of  the  best 
methods  such  material  as  may  be  valuable  for  minute  microscopic 
study.  This,  however,  in  no  way  precludes  the  desirability  of  study- 
ing material  in  a  living  condition  also,  —  whenever  that  is  possible. 

The  material  to  be  preserved  should  be  plunged  into  the  fixing 
solution  in  a  condition  as  fresh  as  possible,  so  that  no  changes  may 
occur  subsequent  to  removal  from  the  natural  substratum.  Great 
haste  is  often  necessary  with  delicate  fungi  in  order  to  avoid  dry- 
ing out.  It  is  well  always  to  use  an  abundance  of  the  fixing  liquid. 
With  osmic  and  chromic  acids  one  should  often  employ  as  much 
as  fifty  times  the  quantity  of  the  liquid  as  of  the  material,  while 
with  alcohol  and  formalin,  fully  three  times  as  much  liquid  as 
material.  In  all  cases,  the  object,  if  large,  should  be  cut  into  pieces 
as  small  as  practicable,  in  |-inch  cubes  or  less. 

Fixing  methods  and  fixing  agents  are  numerous,  and  the  method 
or  agent  to  be  selected  will  depend  upon  the  kind  of  study  for 
which  the  material  is  desired.  One  method  will  be  applicable  when 
histological  differentiation  is  the  chief  end  sought,  and  when  a  study 

4« 


42  CULTURE  METHODS  AND  TECHNIQUE 

of  the  fungous  hyphae  within  other  plant  cells  or  tissues  is  desired  ; 
while  an  entirely  different  method  may  be  essential  if  the  investi- 
gation is  to  concern  itself  with  more  minute  cytological  details. 

Even  when  material  is  to  be  used  for  immediate  casual  study  it 
is  often  necessary  to  kill  and  fix  it  on  account  of  the  greater  ease, 
with  which  the  subsequent  operation  of  staining  may  be  performed. 
In  the  examination  of  hyaline  filamentous  fungi  it  is  unnecessary 
to  use  any  but  the  simplest  methods  of  fixing  on  the  slide.  It  has 
been  found  desirable  to  treat  such  hyphae  for  a  minute  or  two  with 
a  few  drops  of  a  3  per  cent  solution  of  acetic  acid.  This  treatment 
will  also  generally  dispel  bubbles  of  air.  The  acid  should  be  well 
washed  out  with  water  before  using  basic  stains.  In  the  same  way 
a  3  per  cent  solution  of  potassium  hydrate  or  a  weak  solution  of 
chloral  hydrate  will  often  give  good  results,  —  the  former,  particu- 
larly, if  the  material  has  suffered  any  drying  out  and  needs  restor- 
ing by  the  swelling  process  to  which  the  hydrate  is  adapted. 

Alcohol.  The  fixing  qualities  of  alcohol  are  well  known.  When 
employed  alone  it  is  usually  recommended  to  use  either  very  low 
or  very  high  grades  of  this  agent,  and  it  is  serviceable  only  for 
gross  work.  Of  the  lower  grades,  15  to  25  per  cent  are  generally 
used,  for  at  this  concentration  little  harm  will  result  from  the  effects 
of  diffusion  currents.  When  the  higher  grades  are  used,  those 
from  96  per  cent  to  absolute  alcohol  are  preferable,  in  order  to 
effect  rapid  penetration  and  fixing.  Where  the  weaker  grades  are 
employed  first,  the  process  is  also  essentially  one  of  dehydration. 
The  size  and  consistency  of  the  material  will  determine  the  length 
of  time  that  the  object  should  be  left  in  the  lower  grades.  It  is 
usually  left  in  each  lower  grade  from  two  to  four  hours  and  in  each 
higher  grade  from  four  to  twelve  hours.  If  one  begins  with  1 5  per 
cent  alcohol,  the  material  should  subsequently  be  passed  through 
30,  50,  and  70  per  cent,  and  for  safety  in  hardening  85  per  cent, 
and  finally  95  per  cent  may  also  be  used.  Material  that  is  to  be 
kept  for  any  length  of  time  should,  however,  be  stored  in  from  65 
to  75  per  cent  alcohol,  since  the  higher  grades  are  more  apt  to  ren- 
der it  brittle.  If  material  is  fixed  in  from  96  per  cent  to  absolute 
alcohol,  it  may  remain  at  this  concentration  for  from  twenty-four  to 
thirty-six  hours,  and  then,  if  storage  is  desired,  it  should  be  passed 
back  to  the  weaker  grade  mentioned. 


FIXING,  IMBEDDING,  AND   STAINING  43 

Corrosive  sublimate.  Corrosive  sublimate  is  always  an  excellent 
killing  and  fixing  agent  for  histological  staining.  It  may  be  used  as 
a  concentrated  aqueous  solution,  to  which,  also,  the  addition  of  about 
i  per  cent  of  acetic  acid  is  often  helpful.  Whether  the  material  is 
a  fleshy  sporophore,  or  a  piece  of  host  tissue  penetrated  by  hyphae, 
it  should  remain  in  this  fixing  agent  for  about  twenty-four  hours,  or 
until  the  tissue  is  distinctly  white-opaque.  The  material  is  washed 
for  an  hour  or  two  in  water,  and  then  carried  through  the  grades  of 
alcohol,  30,  50,  and  70  per  cent,  and  eventually  stored  in  65-75 
per  cent.  If  not  immediately  imbedded,  it  is  well  to  change  the  70 
per  cent  alcohol  several  times  in  order  better  to  remove  the  subli- 
mate. Sometimes  it  is  necessary  to  add  a  little  tincture  of  iodine 
to  the  alcohol  in  order  to  more  thoroughly  remove  the  corrosive 
sublimate.  If  this  is  done,  the  liquid  should  be  changed  as  often 
as  it  is  discolored  by  the  material.  It  is  also  claimed  that  after  cor- 
rosive sublimate  the  material  should  not  long  be  stored  in  alcohol, 
as  such  material  will  readily  become  brittle. 

It  is  often  preferable  with  fungous  tissue  to  use  a  concentrated 
solution  of  the  sublimate  in  96  per  cent  alcohol,  to  which  it  may 
also  be  well  to  add  I  per  cent  acetic  acid.  This  mixture  penetrates 
more  readily  and  is  more  valuable  for  cytological  work  than  the  aque- 
ous solution.  Objects  thus  fixed  are  transferred  after  from  a  few 
minutes  to  twenty-four  hours  to  lower  grades  of  alcohol,  and  wash- 
ing may  be  effected  by  a  few  changes  at  the  grade  used  for  storage. 

At  laboratory  temperatures  mercuric  chloride  is  soluble  in  water 
to  the  extent  of  about  5  to  6  per  cent,  and  it  is  much  more  soluble 
in  alcohol.  If  it  is  desired  to  use  stronger  solutions  of  the  mer- 
curic salt,  it  will  be  necessary  to  add  to  the  solution  some  chloride, 
such  as  sodium  or  ammonium.  As  will  be  seen  later,  both  the  car- 
mine and  anilin  stains  may  be  used  after  corrosive  sublimate,  and 
the  mixtures  of  this  agent  are  especially  good  for  fixing  parts  of 
any  of  the  fleshy  fungi. 

Chromic  acid  and  chrom-acetic  acid.  Solutions  of  chromic  acid 
from  .5  to  i  per  cent  are  sometimes  used  for  fixing  fungous  mate- 
rial ;  but  in  general  it  is  so  much  less  valuable  alone  than  in 
combination  with  acetic  acid  of  less  or  equal  strength  that  the  com- 
bination should  be  employed.  Wash  and  dehydrate  as  for  the  next 
fixing  agent. 


44  CULTURE  METHODS  AND  TECHNIQUE 

Chrom-osmo-acetic  acid.  This  mixture,  commonly  known  as 
Flemming's  solution,  is  very  satisfactory  for  cytological  work  with 
plant  tissues.  It  is  particularly  desirable  as  a  fixing  agent  to  pre- 
cede the  triple  stain,  also  iron  haematoxylin  ;  and  these  are  two  of 
the  best  cytological  stains.  As  commonly  employed,  the  Flemming 
solution  varies  greatly  in  strength.  The  weaker  solution  is  ordina- 
rily to  be  recommended.  This  should  include  as  an  aqueous 
solution  chromic  acid  from  J  to  \  per  cent,  osmic  acid  ^  per  cent, 
acetic  acid  JQ-  per  cent.  It  is  possible,  however,  to  employ  the 
solution  at  least  twice  as  strong  as  the  formula  given,  and  it  is 
convenient  to  make  stock  solutions  of  each  substance  rather  than 
to  make  up  at  one  time  a  large  quantity  of  the  fixing  fluid.  More- 
over, the  stock  solutions  mentioned  may  be  so  prepared  as  to  serve 
for  any  strength  of  the  Flemming  which  may  be  required.  Stock 
solutions  should  be  as  follows  : 

Chromic  acid I  per  cent 

Osmic  acid i  per  cent 

Acetic  acid I  per  cent 

In  order  to  prepare  the  weaker  fluid,  the  following  quantities 
will  be  required  : 

i  per  cent  chromic  acid  .  .  .  25  cc. 

i  per  cent  osmic  acid      .  .  .  10  cc. 

i  per  cent  acetic  acid      .  .  .  i  o  cc. 

Water     .     .     .     .     .     .  .  .  55  cc. 

Stock  solutions  are  very  desirable  on  account  of  the  fact  that  the 
Flemming  does  not  keep  well,  especially  when  constantly  opened 
for  use.  Any  solution  containing  osmic  acid  turns  black  promptly 
upon  contact  with  certain  organic  material  or  dust.  This  effect  is 
facilitated  by  light,  although  light  alone  is  noninjurious.  It  is 
advisable,  however,  to  store  the  osmic  acid  in  a  brown  bottle,  or  to 
keep  it  from  the  direct  sunlight. 

Ordinarily,  material  should  be  left  in  this  mixture  from  twenty- 
four  to  forty-eight  hours,  and  it  should  then  be  washed  in  running 
water  two  to  four  hours  and  finally  passed  through  the  different 
grades  of  alcohol  beginning  at  1 5  or  30  per  cent  until  the  desired 
storage  grade  is  reached,  or  until  the  material  is  thoroughly  dehy- 
drated, if  it  is  to  be  immediately  imbedded.  After  the  use  of  the 
Flemming  mixture,  however,  it  is  often  necessary  to  decolorize  the 


FIXING,  IMBEDDING,  AND  STAINING  45 

material.  The  decolonization  is  best  effected  when  the  material  is 
in  70  per  cent  alcohol,  and  during  the  dehydration  process.  The 
simplest  method  is  to  add  to  three  parts  of  95  per  cent  alcohol  one 
part  of  hydrogen  peroxide  and  allow  the  material  to  stand  in  this 
mixture  from  twelve  to  twenty-four  hours.  It  seems  to  be  less 
injurious  to  decolorize  in  mass  than  eventually  to  decolorize  the 
sections  on  the  slide,  just  prior  to  staining. 

Alcoholic  mercuro-nitric  acid  solution.  This  fluid  should  be 
more  generally  employed  with  the  fungi,  since  it  penetrates  well, 
and  may  be  advantageously  followed  by  haematoxylin,  anilin,  and 
carmine  stains.  Gelatinous  masses  of  spores  remain  intact  fairly  well 
in  this.  About  300  cc.  may  be  conveniently  made  up  as  follows  : 

Water 270  cc. 

96  per  cent  alcohol ....  30  cc. 

Glacial  acetic  acid    ....  ar  cc. 

Nitric  acid 5  cc. 

Corrosive  sublimate      ...  10  grams     * 

Material  should  remain  in  this  agent  from  one  to  six  hours,  then 
it  may  be  passed  through  grades  of  alcohol  to  70  per  cent,  where 
several  changes  of  the  liquid  should  be  made. 

I  have  not  found  picric  acid,  or  combinations  of  this  with  mer- 
curic chloride  and  other  agents,  satisfactory  for  work  with  the  fungi. 

Formalin  is,  of  course,  a  good  general  preserving  liquid,  but  it  is 
not  practicable  when  imbedding  methods  may  afterwards  be 
employed. 

II.  THE  PARAFFIN   PROCESS:  INFILTRATION  AND 
IMBEDDING 

Material  which  is  to  be  sectioned  by  means  of  the  microtome  is 
now  far  more  commonly  imbedded  in  paraffin  than  in  celloidin  or 
collodion.  Some  chief  advantages  claimed  for  the  paraffin  method 
are  :  ( I )  better  penetration  of  the  imbedding  substance,  permitting 
more  uniform  and  thinner  sections  ;  (2)  facility  in  cutting,  together 
with  ease  of  preserving  the  sections  in  serial  order  ;  (3)  convenience 
of  the  paraffin  ribbon  in  the  further  processes  involved. 

Assuming  that  the  substance  which  is  to  be  imbedded  is  stored 
in  alcohol,  it  becomes  necessary,  as  the  first  step,  to  dehydrate 
thoroughly  by  treating  with  90  per  cent  alcohol  during  about  twelve 


46  CULTURE  METHODS  AND  TECHNIQUE 

hours,  and  then  with  absolute  alcohol.  It  is  desirable  to  change  the 
absolute  alcohol  once,  permitting  the  material  to  remain  each  time 
from  four  to  six  hours. 

The  infiltration  methods,  that  is,  methods  by  which  the  penetra- 
tion of  paraffin  into  the  tissues  and  cells  is  effected,  are  various,  and 
biologists  do  not  agree  as  to  which  is  most  practicable.  The  chief 
difference  lies  in  the  nature  of  the  solvent  employed  to  precede  the 
paraffin.  After  having  tried  for  years  chloroform,  xylol,  and  cedar 
oil  in  turn,  it  is  preferred  with  the  majority  of  tissues  to  employ 
the  chloroform  method,  —  a  method  at  once  simple  and  sure.  It  is 
as  follows  : 

The  chloroform  infiltration  method.  The  material  from  absolute 
alcohol  is  put  into  a  mixture  of  equal  volumes  of  absolute  alcohol 
and  chloroform.  It  is  permitted  to  remain  in  this  mixture  for  from 
twelve  to  twenty-four  hours,  and  then  pure  chloroform  is  sub- 
stituted. In  the  pure  chloroform  readily  penetrable  tissues  will  soon 
sink  and  will  be  thoroughly  penetrated  within  twenty-four  hours. 
Many  tissues  will  require  two  days,  and  two  days  may  be  most 
desirable.  At  the  end  of  this  period,  whether  the  tissue  is  sunken 
or  not,  it  is  poured  out  into  an  open  dish  (small  porcelain  vessels 
2  or  3  centimeters  broad  and  deep  being  very  desirable),  and  into 
this  dish  is  cut  more  than  enough  hard  paraffin  (53°  to  54°  C.) 
finally  to  cover  the  material  with  paraffin  alone,  or,  better,  suffi- 
cient in  which  finally  to  imbed  the  material.  These  dishes  are  then 
put  into  the  oven  at  55°  to  56°  C.  and  the  chloroform  evaporates 
within  a  day  or  two.  If  stirred  once  or  twice,  it  will  evaporate  more 
promptly,  and  the  material  is  then  in  excellent  condition  to  be 
imbedded  in  the  papers  or  special  imbedding  trays  commonly  used. 
Paraffin  used  in  this  process,  if  the  chloroform  has  all  evaporated, 
is  excellent  from  the  standpoint  of  viscosity,  and  consequently  it 
will  cut  more  evenly  than  fresh  paraffin. 

Cedar  oil  and  xylol  infiltration.  Some  prefer  to  use  cedar  oil  as 
a  solvent  with  the  paraffin.  That  method,  however,  is  somewhat 
more  taxing  and  seldom  to  be  recommended.  The  cedar  oil  is 
more  difficult  to  remove  from  the  tissues,  and  I  have  found  it 
desirable  only  in  cases  where  the  material  is  exceptionally  brittle. 
When  cedar  oil  is  employed,  it  seems  desirable  to  pass  from 
absolute  alcohol  to  a  mixture  of  cedar  oil  and  alcohol,  the  tissues 


FIXING,  IMBEDDING,  AND  STAINING  47 

sinking  from  the  alcohol  into  the  cedar  oil,  and  this  indicates  the 
time  when  the  mixture  may  be  replaced  by  pure  cedar  oil.  After 
remaining  in  the  cedar  oil  for  from  twelve  to  twenty-four  hours  soft 
paraffin  may  be  added.  In  from  twelve  to  twenty-four  hours  hard 
paraffin  may  be  used,  and  after  a  similar  period  the  material  may 
be  imbedded  in  trays  in  fresh  paraffin.  It  is  desirable  in  this  proc- 
ess to  have  the  material  held  in  little  wire-meshed  ladles,  and  thus 
the  change  from  one  grade  of  infiltrating  agent  to  another  is  effected 
by  a  transfer  of  the  ladle  from  one  vessel  to  another.  In  each  case 
the  ladle  is  thrust  into  the  liquid  sufficiently  to  cover  the  bowl  and 
material.  The  cedar  oil  is  then  more  readily  displaced,  sinking  to 


FIG.  n.   A  DESIRABLE  OUTFIT  FOR  SECTIONING  AND  STAINING 

the  bottom,  and  there  are  fewer  difficulties  in  sectioning  on  account 
of  electrification,  which  is  intensified  by  the  presence  of  oil. 

Xylol  is  also  employed  in  infiltration,  but  with  some  tissues  there 
seems  to  be  a  peculiar  optical  effect  produced,  and  it  has  no  pecu- 
liar advantages  for  this  purpose. 

Sectioning.  When  the  objects  are  imbedded  they  should  be  so 
disposed  that  each,  or  each  group,  is  far  enough  from  those  adjacent 
co  permit  of  its  being  readily  cut  out  and  attached  to  the  object 
carrier.  When  melted  to  the  carrier  careful  orientation  is  given. 
Sectioning  is  a  simple  operation  with  material  properly  infiltrated, 
with  a  sharp  razor  or  microtome  blade,  and  with  the  laboratory  at 
living-room  temperature.  Very  tough  or  carbonaceous  fungi  will 
never  yield  satisfactory  sections  by  the  paraffin  method,  but  the 
great  majority  of  the  parasitic  fungi  may  be  thus  treated.  There 


48  CULTURE  METHODS  AND  TECHNIQUE 

is  a  tendency  to  make  the  sections  too  thin  when  this  method  is 
employed.  Some  thin  sections  will  usually  be  required,  but  for  such 
studies  as  the  distribution  of  the  fungus  in  the  host,  and  the  forms 
and  relations  of  fruiting  organs,  thicker  sections  are  preferable. 

Attaching  sections.  Since  the  paraffin  method  is  here  presented 
in  some  detail,  a  few  indications  with  reference  to  fixing  sections  to 
the  slide  and  the  further  manipulation  of  the  material  will  be 
requisite.  A  minute  drop  of  egg  albumen  preparation1  is  first 
rubbed  over  that  portion  of  the  slide  to  which  the  sections  are  to 
be  affixed.  Add  a  few  drops  of  water  from  a  pipette,  arrange  the 
sections  or  ribbon  exactly  as  may  be  desired  on  the  slide,  allowing 
for  expansion  to  their  normal  size,  and  place  the  slide  immediately 
in  the  paraffin  oven,  that  is,  at  a  temperature  which  will  just  melt 
the  paraffin  (Strasburger's  method).  In  two  hours  the  slides  will 
be  ready  for  removal  and  for  the  subsequent  processes.  The  method 
mentioned  is  simpler  and  better  than  the  one  in  which  more 
water  is  added  when  the  sections  are  laid  on  the  slide,  the  slide 
warmed  over  a  flame  until  the  sections  spread  out,  the  water  drained 
off,  and  finally  the  slides  set  aside  from  four  to  twenty-four  hours 
to  dry  in  a  warm  place.  In  either  case,  when  the  slides  are 
thoroughly  free  of  moisture,  they  are  passed  into  the  xylol  for  a 
few  minutes,  then  into  absolute  alcohol,  and  to  such  other  grades 
as  are  necessary  prior  to  staining.  In  all  of  these  processes  Cop- 
lin's  staining  jars  or  other  similar  vessels  are  desirable.  Care 
should  always  be  taken  to  remove  every  trace  of  paraffin  before 
proceeding  further. 

III.    STAINING 

Filamentous  fungi.  It  is  often  necessary  to  employ  staining 
methods  in  an  examination  of  hyaline  filamentous  fungi,  even  if 
the  observation  is  merely  for  the  provisional  determination  of  the 
fungus  at  hand.  This  is  particularly  true  in  an  examination  of 
certain  mold  or  hyphomycetous  fungi.  Such  fungi,  and  particu- 
larly the  aerial  parts  of  such  fungi,  should  be  well  teased  out  in  a 
drop  of  weak  acetic  acid,  or  sodium  hydrate  in  10  to  20  per  cent 
alcohol,  on  the  slide.  This  killing  agent  is  drained  off  by  means 
of  filter  paper,  the  preparation  washed,  and  then  it  may  be  stained 

1  Egg  albumen,  50  cc. ;  glycerin,  5  cc. ;  and  salicylate  of  soda,  \  gram. 


FIXING,  IMBEDDING,  AND  STAINING  49 

with  a  solution  of  eosin.  A  J  per  cent  aqueous  solution  will  suffice, 
but  alum  eosin  (1-  per  cent  alum)  is  even  better.  Unless  the  object 
is  first  killed,  as  by  being  treated  with  acid,  the  stain  will  very 
readily  disappear,  or  become  indistinct,  when  mounted  in  glycerin 
"or  in  glycerin  jelly.  A  J-  per  cent  solution  of  fuchsin  may  also  be 
used.  Hyaline  fungi  to  be  preserved  as  glycerin  preparations 
should  always  be  stained,  otherwise  the  fungous  outlines  will  in 
time  become  very  indistinct. 

Many  of  the  fungi  may  be  carefully  studied  for  purposes  of 
identification  and  for  a  knowledge  of  their  general  structure  with- 
out the  use  of  stains  and  staining  methods.  To  this  class  belong 
practically  all  of  the  filamentous  fungi  which  are  not  hyaline,  that 
is,  those  which  are  flavous,  olivaceous,  brown,  or  otherwise  colored 
in  such  a  way  that  the  outlines  of  cell  walls  show  distinctly  when 
mounted  in  water,  glycerin,  glycerin  jelly,  etc.  The  most  delicate 
fungi  are  those  which  necessitate  the  use  of  stains,  such  as  many 
members  of  the  Mucoracece,  Saprolegniacece,  Peronosporacece,  and 
other  related  orders,  as  well  as  many  mucedinous  Hyphomycetes. 

It  is  usually  recommended  to  make  up  concentrated  alcoholic 
solutions  of  eosin  and  fuchsin  as  stock  solutions.  Then,  as  desired, 
weaker  stains  may  be  prepared  from  the  above  by  dilution  with 
water,  the  latter,  of  any  strength  desired,  being  kept  conveniently 
in  dropper  bottles.  The  staining  process  is  very  simple  and  con- 
sists merely  in  adding  a  drop  or  two  of  the  stain  to  the  preparation 
on  the  slide,  then  washing  it  off  with  water  when  the  desired  effect 
has  been  produced.  A  drop  or  two  of  low-grade  or  acidulated  alco- 
hol will  usually  remove  any  overstaining. 

It  has  been  ascertained  that  those  fungi  which  are  stained  only 
with  difficulty  by  this  process  are  much  more  readily  stained  if  an 
acid  or  an  alkaline  solution  of  the  stain  is  employed.  Carbol  fuchsin 
is  one  of  the  recognized  strong  stains  of  this  class.  This  may  con- 
veniently consist  of  a  .5  per  cent  aqueous  solution  of  carbolic  acid, 
to  which  is  added  sufficient  of  the  concentrated  fuchsin  stock 
solution  to  make  a  strong  stain. 

Fleshy  fungi  and  tissues.  Staining  processes  such  as  have  been 
already  described  are  very  simple  when  compared  with  most  of 
those  which  must  be  resorted  to  when  the  material  consists  of  a 
fungous  tissue,  or  of  other  tissue  penetrated  by  a  fungus.  Loose, 


50  CULTURE  METHODS  AND  TECHNIQUE 

readily  penetrable  tissues  may  be  stained  in  mass  with  a  ground 
stain,  but  in  general  it  is  preferable  to  stain  sections  on  the  slide. 
Material  of  the  fleshy  fungi  more  often  lends  itself  to  mass  stain- 
ing, and  this  process  becomes  particularly  desirable,  moreover, 
when  carmine  stains  are  advised.  The  carmine  stains  are  most 
important  if  the  material  has  been  fixed  in  sublimate  mixtures. 

A  successful  method  of  staining  fleshy  fungi  for  histological 
differentiation  has  been  used  by  Burt  as  follows  :  —  Alcoholic 
material  is  stained  in  toto  twenty-four  hours  in  Mayer's  alcoholic 
paracarmine.  When  the  sections  have  been  mounted  on  the  slide 
and  dehydrated,  they  are  stained  for  about  five  minutes  in  an 
aqueous  solution  of  fairly  strong  safranin,  and  finally  washed  in 
water,  previous  to  mounting  in  water  and  glycerin.  With  tissues 
fixed  in  sublimate  mixtures,  the  Ehrlich-Biondi-Heidenhain  stain 
has  also  been  found  to  give  effective  histological  differentiation. 
This  strain  should  be  obtained  ready-mixed  from  Griibler  &  Co. 
To  100  cc.  of  0.4  per  cent  solution  of  this  mixture  must  then  be 
added  7  cc.  of  a  \  per  cent  acid  fuchsin  solution.  This  stain 
gives  some  nuclear  differentiation,  but  it  cannot  by  any  means 
be  called  a  successful  nuclear  stain.  Only  small  quantities  of  this 
stain  should  be  combined  with  the  fuchsin  at  one  time,  since  its 
keeping  qualities  are  not  good. 

A  double  stain  of  any  standard  haematoxylin  followed  by 
erythrosin  eosin  or  orange  G  is  sometimes  to  be  recommended 
when  material  is  fixed  in  alcohol ;  but,  in  general,  many  haema- , 
toxylin  stains  are  not  so  valuable  for  work  with  the  fungi  as  with 
the  higher  plants.  Magdala  or  Congo  red  may  be  followed  by  an 
anilin  blue  or  green  to  advantage.  A  stain  of  any  solution  of  eosin 
or  carmine  followed  by  a  counter  stain  of  nigrosin  is  often  of  value. 
In  cytological  work  more  than  in  any  other  kind,  it  is  necessary 
to  bear  in  mind  the  nature  of  the  fixing  agent  in  deciding  upon 
an  effective  stain.  After  sublimate  fixing,  one  of  the  most  success- 
ful methods  of  staining  on  the  slide  for  the  differentiation  of  cyto- 
plasmic  and  nuclear  structures  is  one  apparently  first  published  by 
Wager.  It  is  a  cumbrous  and  complicated  process  in  print,  but  is 
much  simpler  in  practice.  As  I  have  used  this  stain,  it  is  a  slight 
modification  and  simplification  of  Wager's  process.  The  principal 
solutions  needed  are  : 


FIXING,  IMBEDDING,  AND  STAINING  51 

1 .  A  50  per  cent  solution  of  alcohol  containing  a  trace  of  nigrosin  and  acetic 
acid. 

2.  Mayer's  alcoholic  paracarmine. 

3.  5  per  cent  glacial  acetic  acid  in  50  per  cent  alcohol,  to  which  is  added 
sufficient  nigrosin  to  make  it  bluish  black  in  the  bottle. 

4.  50  per  cent  alcohol  strongly  acidulated  with  acetic  acid. 

The  sections  on  the  slide  are  mordanted  for  a  few  minutes  in 
i.  They  are  then  somewhat  understated  in  solution  2,  the 
superfluous  stain  washed  off  in  50  per  cent  alcohol,  and  the  slide 
placed  in  3.  In  this  last  it  remains  until  examination  shows  it  to 
be  slightly  overstained.  It  is  then  washed  and  decolorized  to  the 
desired  degree  in  the  50  per  cent  alcohol  strongly  acidulated  with 
acetic  acid  (4). 

Mayer's  alcoholic  paracarmine,  used  in  this  connection,  is  made 
by  using  carminic  acid  I  gram,  chloride  of  ammonium  0.3  grams, 
chloride  of  calcium  4  grams,  and  100  cc.  of  70  per  cent  alcohol. 
Dissolve  the  carminic  acid  by  heat  if  desired  for  immediate  use, 
then  allow  it  to  settle,  and  filter. 

Flemming  triple  stain.  When  material  has  been  fixed  in  chromic 
acid  solutions,  particularly  in  the  Flemming  chrom-osmo-acetic,  then 
the  Flemming  triple  stain  is  one  of  the  two  most  valuable  with  the 
fungi,  as  with  nearly  all  other  plant  tissues  similarly  fixed.  This 
stain  requires  safranin,  gentian  violet,  and  orange.  The  usual 
method  is  to  stain  on  the  slide  for  several  hours  to  a  day  in  a 
strong  alcoholic  solution  of  safranin,  rinse  in  95  per  cent  alcohol 
until  very  little  color  remains,  stain  for  a  few  minutes  to  several 
hours  in  gentian  violet,  wash  for  a  very  short  time  in  water,  and 
plunge  into  a  strong  solution  of  orange  G  for  a  few  seconds.  The 
slide  is  then  treated  with  absolute  alcohol  in  order  to  wash  out  the 
surplus  gentian.  Differentiation  is  effected  by  treatment  with  clove 
oil  or  with  clove  oil  first,  and  finally  with  xylol  for  fixing,  before 
being  mounted  in  damar  balsam.  Almost  any  safranin  stain  may 
be  used  in  this  combination,  but  it  will  often  be  found  that  the 
safranin  may  be  entirely  omitted  with  advantage.  By  this  means 
the  process  is  also  greatly  shortened.  Perhaps  the  best  gentian 
violet  which  may  be  used  in  this  process  is  that  of  Ehrlich,  con- 
sisting of : 

Gentian  violet      .      .        i   part           Anilin  oil    ....        3  parts 
Alcohol       ....      15  parts          Water 80  parts 


52  CULTURE  METHODS  AND  TECHNIQUE 

The  method  of  procedure  with  the  gentian  will  depend  on  whether 
a  chromatic  or  a  kinoplasmic  stain  is  desired.  In  the  first  case  a 
short  immersion  in  a  strong  stain  will  give  best  results,  and  in  the 
latter  case  it  is  often  well  to  use  only  a  few  drops  of  the  gentian 
to  a  tumbler  ,of  water.  The  orange  acts  rapidly  upon  well-fixed 
structures,  and  often  an  immersion  of  a  few  seconds  will  suffice. 
Clove  oil  washes  out  the  gentian  somewhat  in  clearing,  but  berga- 
mot  oil  does  not  have  this  effect,  and  serves  rather  to  fix  the  stain, 
30  that  it  may  sometimes  be  necessary  to  dash  the  slide  with  berga- 
mot  oil  before  differentiating  with  clove  oil.  In  every  case,  how- 
ever, considerable  experimentation  is  necessary  for  the  proper 
handling  of  this  stain. 

Iron  hcematoxylin.  Where  the  safranin-gentian-orange  is  in- 
effective, iron  haematoxylin  will  often  give  excellent  results.  With 
this  process  the  sections  are  immersed  from  one  to  several  hours 
in  about  a  3  per  cent  solution  of  iron  alum  (ammonia-sulphate  of 
iron).  They  are  next  washed  well  in  water  and  then  stained  in  a 
0.5  per  cent  aqueous  solution  of  haematoxylin.  The  latter  is  allowed 
to  act  until  a  considerable  overstating  has  resulted.  The  slide  is 
then  washed  and  again  put  into  the  iron  solution  until  the  desired 
differentiation  shall  have  resulted.  It  is  then  dehydrated,  etc.,  as 
usual.  Iron  haematoxylin  will  give  some  brilliant  results  when  the 
Flemming  combination  is  ineffective.  It  is  usually  necessary  to 
considerably  overstain  the  preparations  and  then  to  wash  out 
strongly  in  the  alum  solution  if  chromatin  differentiation  is 
desired.  It  is  sometimes  well  to  follow  this  treatment  with  a 
slight  ground  stain  bf  orange  G. 

After  Merkel's  solution  good  results  have  been  obtained  by 
Harper  with  a  double  stain  of  acid  fuchsin  and  iodine  green.  The 
same  stain  has  also  been  found  useful  after  corrosive  sublimate  by 
Wager  in  his  studies  upon  the  cytology  of  the  yeasts. 

Bacteria.  Only  a  few  general  directions  may  be  given  dealing 
with  some  of  the  ordinary  methods  now  employed  for  the  staining 
of  the  bacteria.  The  concentrated  alcoholic  solutions  mentioned 
for  the  fungi  are  used,  and,  in  addition,  a  similar  solution  of 
gentian  violet.  These  solutions  are  sometimes  made  of  definite  pro- 
portion, standard  strengths  being  I  gram  of  the  stain  to  10  cc.  of 
95  per.  cent  alcohol.  These  solutions  are  diluted  for  use,  just  as  with 


FIXING,  IMBEDDING,  AND  STAINING  53 

the  fungi.  Carbol  fuchsin  is  also  largely  employed  in  the  staining 
of  bacteria.  The  alkaline  stain  most  widely  employed  is  perhaps 
Loeffler's  alkaline  methylene  blue.  This  solution  consists  of: 

Alcoholic  solution  methylene  blue 30  cc. 

i  per  cent  solution  potassium  hydrate  .....          i   cc. 
Distilled  water 100  cc. 

Other  excellent  stains  are  Ehrlich's  anilin-water  fuchsin  and  gentian 
violet.  These  are  made  by  adding  to  10  cc.  of  distilled  water  an 
excess  of  anilin  water ;  this  being  shaken  until  no  more  will  dis- 
solve, and  then  filtered.  To  such  solutions  are  then  added  i  cc. 
of  the  saturated  solution  of  gentian  violet  or  of  fuchsin. 

In  order  to  stain  effectively  the  flagella  of  bacteria  rather  com- 
plex methods  are  necessary.  No  method  is  satisfactory  unless 
every  precaution  is  taken  to  have  (i)  the  cover  slips  thoroughly 
clean  ;  (2)  the  organism  from  a  young  (twelve  to  twenty  hours), 
vigorous  culture,  on  a  suitable  medium ;  and  (3)  the  bacteria 
evenly  and  thinly  disposed  upon  the  slip.  Where  experience  has 
not  taught  one  to  what  extent  to  dilute  a  loop  of  bacteria  for  the 
best  staining  effects,  it  is  well  to  arrange  the  covers  in  series  of 
from  four  to  five.  Place  a  minute  drop  of  water  upon  each  slip, 
then  diffuse  the  bacteria  from  the  culture  in  the  first  drop,  and 
with  a  loop  from  the  first  drop  pass  to  the  second,  third,  etc.,  in 
turn,  first  diffusing  the  contents  of  the  loop,  then  sweeping  the 
needle  across  the  cover  and  passing  to  the  next.  These  are  dried 
and  fixed  to  the  slip  as  previously  indicated. 

There  are  several  important  methods  of  staining  flagella.  Loeffler's 
method,  or  some  modification  of  it,  is  frequently  employed.  This, 
like  most  flagella  methods,  involves  two  chief  operations,  viz.,  mor- 
danting and  staining.  The  mordant  consists  of  : 

20  per  cent  tannic  acid  solution     .     .     .     .     .     .      10  cc. 

Saturated  solution  of  ferrous  sulfate        ....        5  cc. 

Saturated  solution  of  fuchsin,  aq.  or  alcoholic  .     .        i   cc. 

This  mordant  may  be  generally  used  as  above,  or  it  may  be  necessary 
to  add  an  acid  (in  the  case  of  certain  alkali-producing  organisms) 
or  an  alkali  (certain  acid-producing  organisms),  according  to  Loeffler, 
this  being  done  by  adding  to  the  mordant  a  fractional  percentage 
of  weak  stock  solutions  of  a  caustic  alkali  and  an  acid. 


54  CULTURE  METHODS  AND  TECHNIQUE 

A  few  drops  of  the  mordant  are  placed  upon  each  slip  (pref- 
erably supported  by  the  cover  slip  forceps).  The  slip  is  held 
cautiously  high  above  a  small  flame  until  vaporization  begins ;  the 
mordant  is  then  washed  off  with  water,  followed  by  alcohol ;  finally 
the  preparations  are  stained  in  anilin-water  fuchsin,  washed,  dried, 
and  mounted  in  balsam. 

The  modification  of  the  above  stain  by  Lowit  is  strongly  rec- 
ommended. This  consists  in  substituting  copper  sulfate  for  the 
iron  salt.  The  preparations  are  generally  mordanted  from  thirty 
seconds  to  three  minutes  and  washed.  They  may  then  be  stained 
in  the  anilin-gentian  violet  of  Ehrlich  and  the  surplus  stain  washed 
out  in  water,  50  per  cent  alcohol,  or  acidulated  alcohol.  Freshly 
prepared  solutions  both  of  the  mordant  and  of  the  stain  should  be 
employed. 


PART  II 

PHYSIOLOGICAL  RELATIONS 

CHAPTER  III 

GERMINATION  STUDIES 

CLARJC,  J.  F.    On  the  Toxic  Effect  of  Deleterious  Agents  on  the  Germination 

and  Development  of  Certain  Filamentous  Fungi.    Bot.  Gaz.    28  :   289- 

327,  378-404-    1899. 
DUGGAR,  B.  M.    Physiological  Studies  with  Reference  to  the  Germination  of 

Certain  Fungous  Spores.    Bot.  Gaz.    31  :  38-66.    1901. 
FERGUSON,  M.  C.    Germination  of  the  Spores  of   Agaricus  campestris  and 

Other  Basidiomycetous  Fungi.    Bur.  Plant  Ind.  U.  S.  Dept.  Agl.  Built. 

16:    1-43.  pis.  1-3.    1902. 

Requirements  for  germination.  With  regard  to  their  require- 
ments for  germination,  the  spores  of  fungi  show  very  marked 
differences.  It  may  be  possible  to  group  the  fungi  in  three 
categories,  based  upon  their  minimum  requirements,  although 
it  is  very  probable  that  the  limitations  of  these  classes  may 
not  be  fixed  with  any  degree  of  definiteness.  These  classes  are 
as  follows : 

1 .  Those  which  may  germinate  in  moist  air  or  in  water. 

2.  Those  which  require  a  nutrient  solution. 

3.  Those  which  require  a  special  stimulus. 

Where  the  spore  germinates  in  moist  air  or  in  distilled  water  it  is 
merely  the  absorption  of  water,  under  external  conditions  favorable 
for  growth,  which  suffices  to  give  the  necessary  incitation.  In  other 
words,  the  spore  is  then  undoubtedly  provided  with  its  own  food 
material.  Many  parasitic  fungi  evidently  belong  to  this  class.  No 
nutrient  substance  is  known  to  enhance  the  germination  of  spores 
of  the  Uredinales,  Peronosporales,  and  some  other  obligate  parasites. 
This  statement  is  necessarily  put  in  this  form  on  account  of  the 
fact  that  many  observers  have  employed  ordinary  tap  water  in  their 

55 


56  PHYSIOLOGICAL  RELATIONS 

experiments.  Conidia,  aecidiospores,  and  uredospores  ordinarily 
germinate  best  immediately  after  maturity ;  but  oospores  and 
teleutospores  generally  require  a  period  of  rest.  It  is  certain  that 
a  few  saprophytic  fungi  may  also  germinate  in  distilled  water. 
This  is  true  of  (Edocephalum  albidum,  some  species  of  Botrytis, 
and  certain  hyaline-spored  Basidiomycetes. 

In  general,  the  saprophytic  fungi  seem  to  require  a  nutrient 
medium  for  germination  ;  and  the  percentage  of  germination  de- 
pends largely  upon  the  direct  food  value  of  the  medium,  the  per- 
fect food  affording  the  best  germination.  This  is  particularly  true 
for  Penicillium,  Aspergillus,  certain  Mucoraceae,  and  probably 
many  other  fungi.  Moreover,  plant  pathologists  generally  recog- 
nize that  most  of  the  imperfect  or  ascomycetous  parasitic  fungi 
germinate  most  readily  in  nutrient  solutions.  Certain  of  these 
fungi  germinate  best  in  infusions  or  decoctions  of  the  host  plant. 
Excellent  germination  may  occur  in  a  solution  containing  a  single 
nutrient,  as  in  sugar  solution,  glycerin,  a  nutrient  salt,  etc.  Such 
cases  may,  perhaps,  justly  be  classed  among  food  stimuli. 

It  is  known  that  many  parasitic  phanerogams  require  a  special 
stimulus  of  the  host  plant  before  germination  may  be  incited,  and  it 
is  reasonable  to  believe  that  similar  instances  will  be  found  among 
the  fungi.  According  to  De  Bary,  the  hoof  and  feather  fungus, 
Onygena  corvina,  requires  such  a  stimulus.  Very  little  special  work 
has  been  done  along  this  line  of  inquiry,  and  interesting  results 
may  be  expected,  particularly  with  species  which  have  thus  far 
proved  refractory  under  the  usual  methods  of  culture.  Miss  Fergu- 
son has  determined  that  while  Agaricus  campestris  may  germinate 
more  or  less  erratically  in  many  nutrient  media,  or  with  special  stim- 
uli, the  best  and  most  constant  germination  yet  secured  is  obtained 
by  placing  in  the  culture  drop  a  few  strands  of  the  growing  hyphae 
of  the  same  fungus.  In  such  cases,  as  a  rule,  a  germ  tube  of  a  length 
not  greatly  exceeding  the  diameter  of  the  spore  is  emitted,  but  no 
further  growth  results  unless  the  spores  are  transferred.  This 
stimulation  occurs  whether  the  medium  employed  is  a  nutrient 
solution  or  distilled  water.  These  results  I  have  been  able  to  con- 
firm repeatedly.  Moreover,  I  have  found  that  a  similar  stimulus 
to  germination  is  afforded  by  placing  in  the  culture  drop  a  frag- 
ment of  the  fresh  tissue  of  the  sporophore.  The  latter  is  able  to 


GERMINATION.  STUDIES  57 

develop  a  new  growth  upon  which  the  stimulus,  for  the  most 
part,  depends.  In  some  instances  germination  has  been  secured 
in  an  infusion  (implying  no  cooking  or  sterilization)  of  the  fresh 
tissue. 

It  has  been  found  by  Eriksson  that  short  and  sudden  cooling 
has  a  marked  influence  to  increase  the  amount  of  germination  in 
the  aecidiospores  of  the  wheat  rust,  so  that  a  stimulus  from  the 
temperature  relation  may  be  inferred.  It  may  be  well  further  to 
inquire  if  the  "resting"  period  is  essential  to  the  germination  of 
certain  spores.  If  resting  spores  might  be  forced  into  germina- 
tion by  special  stimulation,  pathological  work  might  be  greatly 
facilitated,  and  material  made  available  for  valuable  cytological 
studies. 

Methods  of  study.  Studies  in  the  germination  of  fungous 
spores  in  solutions,  or  in  water,  are  best  made  by  the  use  of  the 
hanging-drop  culture  method  generally  inappropriately  called  the 
Van  Tieghem  cell.  This  method  consists  essentially  in  sowing 
the  spores  in  a  drop  of  the  desired  medium  on  a  cover  glass 
and  then  inverting  this  cover  glass  over  a  glass  ring  cemented 
to  a  glass  slip.  The  old  method  of  using  slides  with  drop  de- 
pressions in  them  is  not  so  satisfactory,  and  cardboard  rings 
give  unreliable  results.  It  is  necessary  to  give  the  details  of  the 
method  referred  to  at  considerable  length.  For  ordinary  pur- 
poses I  have  found  it  desirable  to  use  glass  cylinders  of  15-18 
mm.  internal  diameter  and  9-10  mm.  high,  preferably  16.  x  10 
mm.  Xylonite  rings  produce  products  in^  the  cell  which  may  be 
injurious.  Rings  of  such  size  as  indicated  provide  an  abundance 
of  oxygen,  and  with  them  the  18  or  20  mm.  square  and  round 
covers  are  available.  Round  covers  are  preferred,  since  fewer  acci- 
dents occur  in  using  them.  Slips  and  rings  must  first  be  carefully 
cleaned  by  the  process  previously  mentioned.  In  some  very  deli- 
cate experiments,  where  even  the  vapor  from  vaseline  should  be 
avoided,  rings  may  be  placed  in  a  Petri  dish  provided  with  filter 
paper  in  which  holes  are  cut  for  their  insertion  (Fig.  13,^). 

The  rings  are  cemented  to  the  slips  by  means  of  beeswax  alone, 
or  beeswax  with  the  addition  of  a  small  amount  of  vaseline.1  For 

1  Waterproof  permanent  cements  may  also  be  employed,  but  they  are  not 
generally  satisfactory. 


PHYSIOLOGICAL  RELATIONS 


very  careful  work  purified  beeswax  and  white  vaseline  should  be 
used.  As  a  matter  of  convenience,  two  rings  are  usually  cemented 
to  the  same  slip.  To  make  the  cells,  the  wax  is  kept  melted,  the 
slide  is  slightly  heated  in  the  flame,  and  by  means  of  the  forceps 

the  ring  is  passed  through  the 
flame,  after  which  one  edge 
is  dipped  lightly  into  the 
melted  wax,  then  quickly 
placed  upon  the  .slip.  If  the 
wax  is  too  hot,  it  will  be  nec- 
essary to  touch  the  ring  sev- 
eral times  to  the  melted  wax, 
then  raise  it  high  enough  to 
cool  somewhat.  When  the 
wax  is  cool  the  free  edge  of 
the  cylinder  is  provided  with 
a  ring  of  vaseline  by  invert- 
ing the  cell  over  a  slip,  or 
shallow  watch  crystal,  upon 
which  there  is  spread  a  thin 
layer  of  melted  vaseline  (Fig. 
12).  The  cell  should  be 
momentarily  held  in  this  inverted  position,  or  rested  in  this  position 
on  a  rack,  in  order  that  the  ring  of  vaseline  will  have  some  depth. 
By  means  of  the  vaseline  ring  the  cover  is,  at  the  proper  time, 
cemented  firmly  to  the  glass  cylinder.  If  the  temperature  at  which 
the  cultures  are  to  be  incubated  differs  considerably  from  that  at 
which  the  cells  are  made,  it  has  been  found  well  to  make  with 
the  back  of  a  scalpel  a  small  nick  in  the  vaseline  ring,  through 
which  nick  the  expanding  air  may  pass  when  the  cultures  are 
placed  in  the  thermostat,  or  culture  incubator.  Afterwards  they 
may  be  permanently  sealed  by  slight  pressure  with  scalpel  or 
needle.  A  drop  of  the  culture  fluid  to  be  used  is  placed  on  each 
cover  glass,  and  about  half  a  dozen  drops  of  the  same  fluid  are 
placed  in  the  bottom  of  the  cell.  A  small  glass  rod  is  the  only 
satisfactory  dropper  for  the  first-mentioned  work.  The  drops  are 
inoculated  with  a  few  spores  by  means  of  a  platinum  needle, 
massing  or  bunching  of  the  spores  being  prevented  as  much  as 


FIG.  12.    STAND  AND  DISH  FOR  BEESWAX 


GERMINATION  STUDIES 


59 


FIG.  13.   RINGS  FOR  DROP  CULTURES 
cemented  to  slide  ;  b,  in  Petri  dish  with  filter  paper 


possible.  It  is  sometimes  desirable  to  distribute  the  spores  pre- 
viously in  a  drop  or  sm,n.ll  quantity  of  water,  otherwise  one  may 
get  too  many  in  the  culture  drop.  The  covers  are  then  inverted 
over  the  glass  ring  and  pressed  down  so  as  to  leave  only  one 
minute  unsealed  area. 

It  is  an  unwise  and  an  inaccurate  plan  to  use  in  the  bottom  of 
the  cell  any  other  liquid  than  that  used  in  the  culture  drop.  This 
must  be  so  in  order  that 
there  may  be  no  differ- 
ences of  vapor  pressure, 
and  consequently  no  evap- 
oration  from  drop  to  liquid 
below,  or  vice  versa.  For 
instance,  it  would  be  man- 
ifestly absurd  to  test  ger- 
mination in  a  drop  of,  say, 

^  Per  Cent  alcohol  above  if 

there  were  only  pure  water  below.  If  there  is  danger  of  contami- 
nation below,  and  consequent  interception  of  the  light,  thorough 
sterilization  must  be  given  beforehand.  If  the  drop  cultures  are 
made  as  soon  as  the  slides  are  prepared,  sterilization  should  not 
be  necessary,  since  all  parts  are  flamed.  Sterilization  may  be 
given  at  any  time,  however,  previous  to  the  ringing  with  vase- 
line. It  is  usually  sufficient  to  sterilize  the  cells  in  a  dry  oven  at 
a  temperature  of  from  110°  to  115°  C.  This  temperature  melts 
the  wax,  but  if  the  slides  are  level,  there  is  no  danger  that  the 
cells  will  slip.  A  temperature  much  higher  is  not  to  be  recom- 
mended. Another  convenient  method  of  sterilization  is  by  means 
of  formalin.  The  cells  are  filled  with  a  solution  of  from  3  to  5 
per  cent  formalin,  and  this  is  allowed  to  stand  for  half  an  hour  ; 
then  on  being  rinsed  with  distilled  water,  again  filled  with  the 
water,  and  left  for  ten  minutes  they  will  be  found  sterile.  The 
cells  should  then  be  inverted  and  dried  before  the  ringing  with 
vaseline  is  effected.  By  this  process  some  cells  will  become  dis- 
connected ;  but  if  the  cementing  has  been  well  done,  this  is  a 
matter  of  small  importance. 

Since  it  will  often  be  found  desirable  to  invert  the  slides  and 
cells  to  prevent  contamination  while  awaiting  use,  the  work  should  be 


6o 


PHYSIOLOGICAL  RELATIONS 


done  in  a  culture  room  (Fig.  14),  and  tin  racks  should  be  provided. 
Miss  Ferguson  l  has  devised  a  convenient  stand  for  holding  slides 
in  cell  culture  work  ;  and  since  in  many  laboratories  where  infection 
experiments  are  made,  or  where  physiological  work  is  done,  large 
numbers  of  these  cells  may  be  used,  this  stand  becomes  a  very  use- 
ful device.  It  has  been 
described  as  follows  : 

A  stand  for  hanging-drop 
cultures.  A  stand  for  support- 
ing slides  when  one  is  using 
the  Van  Tieghem  cells  should 
be  made  of  such  material  and 
in  such  a  way  that  it  will 
neither  burn,  warp,  nor  melt 
upon  being  heated,  for  it  is 
often  desirable  to  sterilize  the 
cells  before  making  up  the 
cultures.  It  should  also  com- 
bine economy  of  space  with 
ease  of  manipulation.  All 
these  points  are  characteristic 
of  the  little  piece  of  apparatus 
which  I  have  used.  .  .  . 

This  stand  consists,  as  will 
be  seen  from  the  photographs 
.  .  .  ,  of  a  series  of  trays 
placed  one  above  the  other. 
Each  tray  was  made  from  a 
single  piece  of  tin  without  the 
use  of  solder.  The  tin  meas- 
ured 13^  by  3}  inches  after  it 
was  hemmed.  This  was  folded 
on  the  sides  just  as  one  folds 

a  piece  of  paper  in  making  the  boxes  described  by  Lee  ( 1 896)  for  imbedding 
material  in  paraffin.  A  strip  i }  inches  wide  along  both  ends  and  on  one  side 
was  bent  up  at  right  angles  to  the  rest,  so  that  a  box  open  at  the  top  and  along 
one  side  was  formed,  which  measured  1 1  by  2|  inches  on  the  bottom.  The 
double,  triangular,  carlike  projections  formed  at  the  two  corners  were  folded 
along  the  back  and  secured  by  means  of  rivets.  The  tin  was  then  cut,  or 
slashed,  f  of  an  inch  deep,  i  inch  distant  from  either  corner  on  the  back. 
Similar  cuts  were  also  made  at  the  corners,  and  three  equally  distant  from 
each  other  and  from  the  outer  edges  were  made  on  either  end.  The  segment 


FIG.  14.    A  SMALL  CULTURE  ROOM,  CONVEN- 
IENT AND  EASILY  CLEANED 


1  Fergusor,  M.  C.    Bureau  Plant  Industry,  Built.  16,  /. 


GERMINATION  STUDIES  6 1 

of  tin  along  the  middle  of  the  back  and  those  next  to  the  free  outer  segments 
on  the  ends  were  folded  in  vntil  parallel  with  the  bottom.  These  act  as  a  shelf 
on  which  to  rest  the  next  higher  tray.  The  outer  and  innermost  segments  at 
both  ends  were  bent  outward,  forming  projections  which  are  very  useful  in 
lifting  the  trays.  The  second  segment  from  the  corner  at  either  end  was  bent 
out  at  right  angles  to  the  side,  and  then  the  outer  portion  of  it  was  again  turned 
up  until  it  was  parallel  with  the  position  which  it  formerly  occupied.  These,  with 
the  segments  at  both  corners  along  the  back,  which  were  left  erect,  prevent  the 
next  higher  tray  from  slipping  or  sliding.  It  was  found  desirable  to  cut  the. 
bottoms  of  the  trays  out,  since  the  rapid  absorption  of  heat  by  the  tin  has  a  tend- 
ency to  increase  the  condensation  moisture  on  the  cover  glasses. 

For  convenience  in  use  it  is  necessary  that  trays  be  about  \  inch  narrower 
than  the  slides  are  long.  Unfortunately,  the  slides  thus  extending  over  the 
edges  of  the  pans  are  very  easily  struck,  and  the  cultures  thereby  endangered 
when  one  is  putting  other  material  into  or  taking  it  out  of  the  thermostat.  To 
guard  against  such  accident,  as  well  as  for  greater  ease  in  carrying,  a  bottom 
tray  was  made  \  inch  wider  than  the  others,  and  with  a  back  5^  inches  high. 
This  tray  had  five  segments  cut  at  each  end  instead  of  four,  and  these  were 
turned  the  same  as  in  the  other  trays,  except  that  the  outermost  one  was 
bent  in  to  give  greater  stability.  Shelves  were  made  along  the  back  by  cut- 
ting and  folding  in  the  tin  at  these  points.  The  windows  thus  formed  give 
free  circulation  of  air.  These  windows,  each  2\  inches  long  and  i  inch  deep, 
were  so  cut  that  if  the  pieces  of  tin  freed  along  three  sides  had  been  bent 
straight  inward,  they  would  have  formed  shelves  \  inch  higher  than  those  at 
the  ends.  But  they  were  doubled  in  close  against  the  back  for  an  inch,  and 
then  turned  out  until  they  stood  parallel  with  the  bottom  of  the  tray.  This 
gives  a  little  back  at  the  points  where  the  windows  occur,  and  prevents  any 
cultures  on  the  second  tray  from  slipping  through  these  open  spaces.  For 
convenience  in  handling,  the  bottom  was  not  cut  from  this  first  tray  as  from 
the  others,  and  it  may  be  used  for  a  support  for  cultures  or  not,  at  the  discre- 
tion of  the  operator. 

The  trays  were  all  made  of  the  same  size.  Five  trays  besides  the  bottom  one 
constitute  a  "set"  as  we  have  used  them.  Each  such  set  holds  120  cultures, 
and  occupies  only  36  square  inches  of  space  in  the  thermostat.  The  trays  may, 
of  course,  be  made  of  any  length  or  of  any  height,  the  dimensions  given  are 
those  best  suited  to  the  thermostat  which  we  have  used.  When  all  the  trays 
have  been  filled  in  making  up  a  set  of  cultures  the  five  upper  ones  are  lifted 
together  and  so  placed  on  the  lowest  pan  that  their  open  sides  were  against 
the  back  of  this  tray. 

I  am  aware  that  the  number  of  words  necessary  for  describing  this  little 
piece  of  apparatus  makes  it  appear  somewhat  complicated,  but  if  one  will  take 
a  piece  of  paper  of  suitable  dimensions  and  follow  the  description  given,  he 
will  find  that  the  making  of  a  model  of  one  of  these  trays  is  a  very  simple 
matter, 


CHAPTER  IV 

GENERAL  RELATIONS  TO  ENVIRONMENTAL  FACTORS 

BENECKE,  W.  Allgemeine  Physiologic  der  Ernahrung  der  Schizomyceten 
und  der  Eumycetem  (Stoffwechsel).  Lafar's  Hdb.  d.  tech.  Mykologie  1 : 
303-427. 

I.    SAPROPHYTISM  AND  PARASITISM 

Since  the  fungi  are  those  classes  of  plants  low  in  the  series  with 
respect  to  morphological  complexity  which  possess  no  chlorophyll, 
they  are  unable  to  utilize  the  carbon  dioxid  of  the  air,  and  like  in- 
sects and  other  animals  they  require  their  carbon  in  organic  com- 
binations. They  are  accordingly  associated  with  organic  matter, 
living  or  dead.  The  plant  pathologist  devotes  primary  attention  to 
those  fungi  inducing  injuries  sufficient  to  be  termed  plant  diseases. 
Interest  is,  of  course,  attached  also  to  any  parasitic  species ;  that 
is,  to  any  which  may  penetrate  and  develop  within  or  upon  the 
tissues  of  another  plant,  but  the  nature  and  extent  of  the  disturb- 
ances which  result  offer  the  special  problems  and  make  necessary 
the  special  field  of  the  pathologist. 

The  habitats  of  the  majority  of  the  fungi  are  situations  in  which 
organic  matter  is  available  through  the  decay  of  dead  things.  In- 
deed the  fungi  take  a  prominent  part  in  decay,  or  the  return  of 
organic  matter  to  more  elementary  combinations.  Forest  and  field, 
therefore,  abound  in  species,  whether  evident  or  not  to  the  popu- 
lar eye.  The  fungi  associated  with  decaying  materials  only  are 
termed  saprophytes  (metatrophs}.  Theoretically,  the  pathologist  is 
not  concerned  with  this  class  of  organisms.  On  the  other  hand, 
a  very  considerable  part  of  the  fungi  obtain  their  organic  nutrients 
by  penetrating  a  living  organism  as  host  and  growing  in  inti- 
mate association  with  its  body.  Such  fungi  are  termed  parasites 
(paratrophs}.  The  parasitic  fungi  are,  for  the  most  part,  parasitic 
upon  plants,  although  small  groups  are  confined  very  largely  to 
insects,  and  a  few  species  affect  higher  animals. 

62 


ENVIRONMENTAL  FACTORS  63 

Considering  the  fungi  as  a  whole,  there  is  necessarily  no  sharp 
line  of  demarcation  between  the  saprophytic  and  the  parasitic  habit. 
Some  organisms  which  attain  their  best  development  as  parasites 
may,  if  occasion  demands  it,  sustain  themselves  saprophytically, 
or  they  may  normally  undergo  a  portion  of  their  existence  as  sapro- 
phytes. The  converse  of  this  is  also  true.  With  respect  to  this 
habit  four  subdivisions  may  be  recognized. 

Obligate  parasites  are,  practically  speaking,  entirely  dependent 
upon  other  living  things  for  requisite  conditions  of  growth  and 
particularly,  perhaps,  for  the  organic  nutrients. 

Obligate  saprophytes  grow  upon  nonliving  substances  and  are 
unable  to  penetrate  living  tissues. 

Facultative  saprophytes  are  organisms  which  normally  pass 
through  life  as  parasites,  but  which  are  capable  for  a  time,  or  in 
certain  stages  of  development,  of  a  true  saprophytic  existence. 

Facultative  parasites  are  saprophytes  which  only  occasionally, 
or  under  very  special  conditions,  may  become  parasitic. 

In  making  these  distinctions  it  should  not  be  assumed  that 
special  weight  is  given  to  the  form  of  the  organic  food  materials 
utilized  by  the  fungus,  since  it  is  quite  probable  that  a  parasite  on 
the  one  hand  and  a  saprophyte  on  the  other  may  secure  from  its 
host  or  from  the  substratum  precisely  the  same  compounds.  Bio- 
logical relations  should  be  regarded  as  most  important.  For  general 
descriptive  purposes  and  for  biological  discussion  the  classification 
mentioned  above  is  a  matter  of  convenience,  but  opinions  would  vary 
greatly  if  it  were  necessary  to  apply  this  specifically. 

The  group  in  which  obligate  parasitism  seems  most  clearly  de- 
fined is  that  of  the  rusts,  Uredinales.  It  would  be  useless  to  try  to 
cultivate  these  fungi  in  nonliving  substrata,  that  is,  in  artificial 
cultures.  The  germination  of  the  spores  alone  may  proceed  apart 
from  the  host.  In  such  groups  as  the  Chytridiales  and  the  downy 
mildews,  Peronosporaceae,  the  majority  are  obligate  parasites ;  yet 
a  few  of  the  former  order,  and  species  of  Phytophthora  in  the 
latter  family,  have  been  grown  on  dead  substrata.  The  smuts, 
Ustilaginales,  and  the  plum  pockets  and  witches'  brooms  of  stone 
fruits,  Exoascaceae,  are  strictly  parasitic,  although  upon  artificial 
media  the  conidia  of  many  species  may  sprout  vigorously.  The  sur- 
face mildews,  Erysiphaceae,  are  doubtless  also  properly  classed  here. 


64  PHYSIOLOGICAL  RELATIONS 

The  obligate  saprophytes  include  many  of  the  mushrooms, 
Basidiomycetes,  and  common  molds  of  diverse  families. 

Most  of  the  important  disease-producing  fungi  popularly  known 
as  leaf  spots,  cankers,  stem  rots,  etc.,  are  capable  of  vigorous 
growth  in  artificial  culture,  and  some  even  produce  normal  fruit 
bodies  under  such  conditions.  These  fungi  are  commonly  Asco- 
mycetes  and  Basidiomycetes.  In  nature  many  organisms  belong- 
ing to  these  classes  develop  and  mature  their  fruit  bodies,  especially 
the  perfect  stages,  only  after  the  infested  parts  are  dead  and 
fallen. 

The  facultative  parasites  are  found  especially  among  the  groups 
mentioned  in  the  last  paragraph  and  also  among  the  black  molds, 
Mucoraceae.  Fungi  which  are  ordinarily  common  upon  decaying 
logs,  or  destructive  to  timber,  may  occasionally  develop  as  para- 
sites on  living  trees.  The  black  mold,  Mucor  mucedo,  so  common 
in  the  household,  may  under  certain  conditions  cause  a  serious  rot 
of  sweet  potatoes,  and  it  has  been  known  to  injure  some  plants  in 
the  seedling  stage.  The  conditions  under  which  such  saprophytes 
become  parasitic  are  not  always,  clearly  understood.  In  general  it 
is  evident  that  some  condition  of  the  environment  has  operated  to 
render  the  host  plant  less  resistant,  or  else  the  conditions  have 
been  such  as  to  develop  exceptional  vigor  in  the  fungus.  Almost 
as  long  as  fungous  diseases  have  been  known  there  has  existed 
the  belief  that  such  diseases  in  any  given  host  plant  are  in  some 
way  dependent  upon  a  certain  lack  of  vigor  in  the  plant.  Practical 
growers  and  many  plant  pathologists  have  held  that  vigorous,  well- 
cultivated,  and  well-nourished  plants  mean  plants  resistant  to  disease. 
No  one  would  question  the  general  desirability  of  resistant  plants, 
yet  this  attitude  requires  special  comment  and  treatment. 

A  very  large  number  of  the  obligate  parasites  and  some  fungi 
less  obligatorily  parasitic  are,  or  seem  to  be,  specially  endowed  with 
the  ability  to  enter  relatively  vigorous  growing  organs  of  the  plant. 
The  majority  of  the  fungi,  moreover,  do  not  kill  immediately  the 
tissues  which  they  invade.  All  sorts  of  deformities,  including 
witches'  brooms,  may  appear  as  a  result  of  the  association  ;  but  so 
long  as  the  fungus  is  rapidly  growing,  it  seems  generally  to  have 
a  well-established  relation  with  the  living  cells,  such  that  when  the 
invaded  tissues  die,  the  fungus  spends  itself  in  reproduction. 


ENVIRONMENTAL  FACTORS  65 

In  contrast  to  those  just  mentioned,  there  is  that  general  sub- 
division of  diseases,  which  we  have  designated  as  leaf  spots,  stem 
rots,  and  fruit  decays.  The  fungi  producing  these  affections  fre- 
quently, though  by  no  means  always,  kill  the  tissues  as  they  pene- 
trate the  host.  In  other  cases  they  enter  and  produce  disease  only 
when  the  affected  parts  have  suffered  some  injury,  overstimulation, 
or  drying  out.  In  the  case  of  fruits  they  are  proverbially  destructive 
when  the  fruits  approach  maturity.  In  other  words,  a  very  large 
number  of  the  fungi  here  included  are  not  in  very  close  associa- 
tion with  living  tissues,  and  are,  from  several  points  of  view, 
hemiparasitic.  It  is  to  be  emphasized,  however,  that  many  of  our 
disastrous  fungous  diseases  are  included  in  this  subdivision.  Now 
in  the  case  of  the  strictly  parasitic  fungi  already  referred  to,  it  is 
very  doubtful  if  vigor  of  the  host  is  alone  sufficient  to  prevent 
disease.  In  fact,  some  of  the  most  vigorous  varieties  (whether 
judged  by  vegetative  or  fruiting  achievements)  have  been  particu- 
larly susceptible  to  certain  diseases.  Before  adopting  the  view  that 
all  ills  flee  before  vigor  we  must  make  ourselves  clear  as  to  what 
vigor  means.  If  it  is  synonymous  with  resistance  to  disease,  then 
of  course  all  plants  subject  to  disease  under  any  conditions  are 
nonvigorous.  Many  wild  or  native  prototypes  of  certain  highly 
responsive,  cultivated  varieties  when  grown  side  by  side  with  the 
latter  may  show  more,  or  may  show  less  resistance  to  disease, 
wholly  independent  of  robustness.  It  does  not  at  all  hold  that 
factors  which  favor  the  fullest  development  of  the  host  may  not 
also  encourage  the  fungus.  Moreover,  factors  unfavorable  to  the 
host  may  be  similarly  unfavorable  to  the  fungus. 

Phytophthora  infestans,  Plasmopara  Viticola,  and  Cystopus  can- 
didus,  on  some  of  their  hosts,  —  the  potato,  the  grape,  and  the 
shepherd's  purse  respectively,  —  would  seem  often  to  be  most 
effective  when  the  host  is  growing  vigorously.  Ward  has  suggested 
from  experiments  with  the  rust  on  brome  grass  that  any  hindrance 
tp  free  nutrition  of  the  host  is  likewise  a  means  of  inhibiting  the 
fungus. 

In  the  case  of  fungi  whose  weapons  for  attack  are  most  effectr 
ive  where  the  plant  is  least  alive,  so  to  speak,  —  as  when  the 
leaves  have  been  injured  by  drought  or  other  causes,  or  when  the 
fruit  is  maturing,  —  it  is  then  clear  that  any  environmental  factor 


66  PHYSIOLOGICAL  RELATIONS 

promoting  a  healthy  growth  of  all  parts  of  the  host  throughout  the 
season  would  decrease  disease. 

After  all,  saprophytism  and  parasitism  are  terms  of  degree,  and 
organisms  are  classed  as  possessing  the  one  habit  or  the  other 
simply  upon  general  evidence,  or  macroscopic  appearances.  It  is 
quite  possible,  however,  that  in  an  ultimate  analysis  of  the  associa- 
tion of  host  and  parasite,  or  of  the  method  of  fungous  attack, 
many  organisms  now  regarded  as  parasitic  would  be  found  to  show 
a  true  saprophytic  habit.  It  is  possible  that  such  organisms  may 
gain  entrance  to  the  host  through  injuries ;  in  other  words,  estab- 
lish themselves  in  association  with  dead  cells.  By  growth  in  these 
cells  the  excretion  of  acids  and  other  diffusible  products  might 
bring  about  death  in  other  cells  in  the  vicinity,  to  which  the  fungus 
eventually  spreads.  So  far  as  the  actual  presence  of  the  fungus  is 
concerned,  therefore,  there  would  be  no  direct  association  with  a 
living  cell  in  order  to  secure  organic  nutrients.  This  method  of 
attack  has  been  demonstrated  to  be  that  followed  by  Botrytis  cinerea, 
a  common  greenhouse  fungus. 

II.    GENERAL  RELATIONS  TO   CLIMATOLOGICAL  FACTORS 

Experiment  and  observation  alike  demonstrate  that  the  abun- 
dance of  a  very  large  number  of  fungous  diseases  is  directly  con- 
nected with  or  conditioned  by  climatological  factors.  With  respect 
to  conditions  in  the  open,  climatological  factors  are  generally  under- 
stood to  mean  water  (moisture),  light,  temperature,  and  wind. 
These  factors  may  affect  independently  host  and  parasite,  and  they 
may  affect  the  interrelations  of  these  organisms.  Moreover,  it  is 
often  difficult  to  interpret  what  factor  is  finally  operative,  or  it  is 
difficult  to  determine  what  are  direct  and  what  indirect  effects  of 
these  environmental  conditions  upon  host  and  fungus.  In  many 
instances  it  would  be  merely  hypothetical  with  the  data  at  hand  - 
largely  observational  —  to  do  more  than  designate  certain  apparent 
or  proximate  causes. 

Moisture.    Many  fungous  diseases  are  directly  associated  with 
abundant  precipitation,  or  a  humid  atmosphere.    There  is  no  more 
conspicuous  example  of  this  than  the  brown  rot  of  stone  fruits  - 
a  disease  which,   in  moist   weather,   has  repeatedly  crippled  the 
peach  industry.    The  association  of  epidemics  of  such  diseases  as 


ENVIRONMENTAL  FACTORS  67 

black  rot  of  the  grape,  apple  scab,  and  late  blight  of  the  potato 
with  humidity  is  a  matter  of  almost  annual  record. 

Moisture  generally  augments  the  production  of  spores,  and  it  is, 
of  course,  essential  to  the  germination  of  these.  It  may  at  times, 
however,  have  another  effect,  —  that  of  promoting  the  suscepti- 
bility of  the  host  to  attack.  The  potato  appears  to  be  more  readily 
affected  by  the  Phytophthora  when  it  has  at  least  sufficient  water 
for  vigorous  growth.  Kiihn  observed  that  there  are  two  stages  of 
growth  when  the  plant  is  most  susceptible,  first,  when  the  plant  is 
young  and  tender,  and  second,  when  tuber  formation  begins  more 
vigorously.  Ward  thinks  these  two  stages  correspond  to  periods 
of  rapid  movement  of  water  and  soluble  food  materials. 

He  has  also  cited  certain  conditions  under  which  Botrytis  cin- 
erea  is  parasitic,  and  the  suffusion  of  the  host  with  water  is  a 
prominent  feature  of  this  case. 

It  is  commonly  stated  by  grape  growers  that  not  only  is  the 
black  rot  of  this  fruit  most  abundant  in  humid  weather,  but  that, 
further,  it  is  more  abundant  upon  vines  which  have  made  a  vigor- 
ous "  sappy  "  growth.  This  would  indicate  that  moisture  acts  here 
also  indirectly  to  render  the  host  more  sensitive. 

Pseudomonas  campestris,  producing  the  black  rot  of  cabbage, 
gains  entrance  to  its  host  by  reason  of  beads  of  water  over  the 
marginal  water  pores  of  the  leaf.  These  droplets  are,  when  there 
is  sufficient  soil  moisture,  a  normal  occurrence  on  cool  mornings 
succeeding  warm  days.  It  signifies  a  state  of  "guttation,"  and, 
practically  speaking,  means  a  water  way  between  the  external  and 
internal  environment. 

Smith  and  Stone  (see  asparagus  rust)  have  demonstrated  an 
interesting  water  relation  as  affecting  the  prevalence  of  the  rust  of 
asparagus.  The  fact  that  chrysanthemum  rust  may  be  largely 
controlled  by  subirrigation,  and  carnation  rust  greatly  reduced  by 
the  same  treatment,  is  perhaps  to  be  explained  simply  by  the 
prevention  of  germination. 

An  examination  of  the  conditions  under  which  epidemics  occur 
in  the  case  of  such  fungi  as  the  leaf  blight  of  celery,  leaf  spot  of 
strawberry,  and  many  others  lead  to  some  interesting  suggestions. 
These  diseases  may  disappear  during  a  moist  summer,  which 
affords  a  relatively  succulent  growth  of  the  hosts.  In  fact,  such 


68  PHYSIOLOGICAL  RELATIONS 

blights  mentioned  seem  to  profit  materially  from  severe  alterna- 
tions or  contrasts  of  weather  conditions.  Moreover,  if  heavy  dews 
prevail  during  a  warm  summer  these  fungi  spread  irrespective  of 
precipitation.  In  such  cases  it  is  apparent  that  injured  or  drying 
portions  of  the  plant  are  at  least  the  first  seats  of  disease.  It  seems 
to  be  true  that  many  crop  diseases  are  commonly  most  important 
under  conditions  of  moisture  insufficient  for  most  vigorous  crop 
production. 

Light.  The  chief  r61e  of  light  in  plant  economy  is  connected 
with  the  formation  of  sugar  and  starch,  from  which,  in  large  part, 
the  other  organic  products  are  ultimately  derived.  Light,  how- 
ever, calls  forth  a  variety  of  responses  in  every  green  plant,  and 
it  may  play  a  direct  or  indirect  role  in  the  relation  with  parasitic 
fungi.  It  has  long  been  observed  that  celery  under  lath  or  cloth 
screens,  that  is,  half  shade,  is  largely  free  from  the  early  blight. 
The  leaf  spot  or  so-called  rust  on  the  strawberry  may  be  similarly 
controlled  through  reduction  of  the  light  factor  with  the  increased 
humidity  and  diminished  evaporation  generally  incident  thereupon. 
It  is  also  reported  that  the  tent  cloth  is  effective  against  asparagus 
rust.  Ginseng  growers  in  New  York  and  Missouri  are  employing 
the  lath  screen  advantageously  in  the  prevention  of  a  serious  blight 
of  this  plant,  due  to  a  fungus  which  is  believed  to  gain  entrance 
most  readily  at  the  margin  of  the  leaf,  possibly  following  a  tend- 
ency to  sun  scald  in  that  area.  Screening,  however,  is  not  advised 
for  strawberries,  and  it  would  be  available  in  the  home  garden,  in 
general,  only  where  such  a  device  may  be  at  will  readily  interposed 
or  removed.  In  opposition  to  these  beneficial  effects  of  half  shade, 
we  have  also  abundant  observations  showing  that  certain  powdery 
mildews  are  far  more  effective  as  parasites  under  just  such  con- 
ditions as  above  enumerated.  I  have  seen  wheat  under  partial 
shade  badly  infested  with  the  powdery  mildew,  which  in  the 
central  West,  at  least,  is  seldom,  if  ever,  seen  in  the  open.  Time 
and  again,  in  that  same  region,  one  may  observe  that  in  the  case 
of  well-watered  lawns  the  mildew  of  blue  grass  abounds  in  a  circle 
rather  sharply  limited  by  the  heavier  shadow  areas  of  trees.  Simi- 
larly, in  the  drier  West  the  grape  mildew  is,  as  a  rule,  found  mostly 
on  Vitis  vinifera  stock,  and  in  shaded  places.  The  fungus  soon 
disappears  from  leaves  to  which  strong  sunlight  is  admitted. 


ENVIRONMENTAL  FACTORS  69 

Strawberry  mildew  is  also  far  more  abundant  in  shaded  localities. 
It  is  a  matter  of  common  observation  that  while  cucumbers  fre- 
quently mildew  under  greenhouse  conditions,  yet  in  the  open  the 
cucumber  mildew  is  very  seldom  observed  upon  this  host,  at  least 
in  the  eastern  and  central  United  States.  It  is  claimed  that  cer- 
tain greenhouse  plants  are  more  subject  to  the  attack  of  the  com- 
mon gray  mold,  Botrytis,  when  partially  etiolated,  and  De  Bary,  it 
seems,  was  able  to  predispose  Petunia  to  the  attack  of  Botrytis 
through  etiolation. 

It  is  apparent  that  in  so  far  as  screen  mechanisms  largely  pre- 
vent the  formation  of  dew,  it  is  probably  in  large  part  through 
this  change  in  the  moisture  relation  that  they  are  important. 
There  may  also  result  a  number  of  direct  effects  of  light,  for 
in  the  case  of  strongly  etiolated  or  yellowed  and  attenuated 
plants,  bud  and  stem  diseases  seem  frequently  to  be  more  com- 
mon. Very  little  experimental  study  has  been  bestowed  upon 
these  relations. 

III.  SPECIAL   RELATIONS   TO   ENVIRONMENTAL   FACTORS 

Temperature.  Very  little  work  has  been  done  which  bears 
more  particularly  upon  the  relation  of  parasitic  fungi  to  various 
conditions  of  environment  than  to  fungi  in  general.  The  results 
of  the  work  available,  however,  will  be  of  assistance  to  the  stu- 
dent and  investigator  in  using  his  culture  work  to  the  greatest 
advantage. 

The  optimum.  The  optimum  temperature  for  growth  of  a 
particular  fungus  in  culture  may  not  be  the  optimum  tempera- 
ture for  spore  germination  or  for  spore  formation.  It  is  difficult 
for  observers  to  agree  precisely  in  giving  what  is  termed  the 
optimum  temperature  for  any  fungus,  since  one  observer  may 
emphasize  the  total  growth  (dry  weight),  another  the  abundance 
of  spore  production,  etc.  The  optimum  temperature  as  given 
for  the  growth  of  various  species  of  bacteria  usually  refers  to 
the  temperature  at  which  the  extent  of  the  colony  is  greatest. 
Wiesner  has  studied  in  detail  the  relation  to  temperature,  of 
(a)  germination,  (b)  visible  mycelium  development,  and  (c)  spore 
formation  in  the  saprophytic  fungus  Penicillium  glaucum.  In 
the  absence  of  data  equally  as  good  for  parasitic  fungi,  the 


PHYSIOLOGICAL  RELATIONS 


observations  on  the  above-mentioned  organism  are  here  presented 
in  tabular  form. 


Temperature,  °  C. 

Time  to  Germination 
(Days) 

Time  to  Production 
of  Visible  Mycelium 
(Days) 

Time  to  Spore 
Formation 
(Days) 

i-5 

5.80 

2.O 

5-5° 

2-5 

3.00 

6.00 

3-° 

2.50 

4.00 

9.00 

3-5 

2.25 

3-50 

8.00 

4.0 

2.OO 

3.00 

7-75 

5-o 

1-50 

2.90 

7.00 

7.0 

1.  2O 

3.00 

6.25 

II.O 

I.OO 

2.30 

4.00 

14.0 

0.75 

2.OO 

3.00 

17.0 

0.75 

2.OO 

3.00 

22.O  (Opt.) 

0.25 

I.OO 

1.50 

26.O 

0.50 

0.99 

2.OO 

32.0 

0.70 

I.OI 

2.IO 

38.0 

o-55 

2.25 

2.60 

40.0 

0.70 

2.50 

3-5° 

In  the  above  case  it  happens  that  the  optimum  for  germination 
corresponds  very  closely  with  that  for  the  formation  of  a  visible 
mycelium  and  for  the  beginning  of  spore  production,  but  this  will 
not  hold  for  all  fungi.  In  general,  the  optimum  temperature  for 
the  bacteria  and  fungi  with  which  the  pathologist  is  concerned 
would  lie  between  25°  and  32°  C.,  and  it  is  customary  to  run  an 
incubator  in  which  ordinary  cultures  are  being  kept  for  vigorous 
growth  and  development  at  from  26°  to  28°  C. 

High  temperatures.  The  thermal  death  points  for  vegetative 
cells  of  the  bacteria  and  fungi  have  been  variously  determined 
to  range  from  40°  to  75°  C.  As  a  rule,  few  fungi  will  grow 
above  40°,  and  to  this  temperature  most  of  these  organisms  will, 
after  a  time,  succumb.  Nevertheless,  both  fungi  and  bacteria  are 
able  in  one  stage  or  another  to  survive  considerable  extremes  of 
heat  and  cold.  The  parasitic  organisms  in  general  are  vegeta- 
tively  vigorous  within  far  narrower  limits  than  those  of  sapro- 
phytic  origin,  which  latter  are,  for  the  most  part,  in  nature 
subjected  to  greater  extremes  of  conditions  during  the  growing 
period. 


ENVIRONMENTAL  FACTORS  71 

It  is  well  known  that  spores  of  bacteria,  unlike  the  vegetative 
cells,  are  extremely  resistant  to  heat,  —  an  exposure  of  one  or  two 
hours  at  the  boiling  point  often  fails  to  kill  the  more  resistant 
forms.  Likewise,  it  has  been  supposed  that  spores  of  fungi  are 
similarly  more  resistant  than  the  vegetative  condition.  This  has 
not  been  found  to  be  true  in  the  case  of  Sporotrichum  globu- 
liferum?-  and  it  was  demonstrated  in  my  laboratory  that  spores 
(conidia)  of  five  forms  —  Aspergillus  niger,  Aspergillus  flavtis, 
Penicillium  sp.,  Botrytis  vulgaris,  and  Rhizoptis  nigricans — differ 
very  slightly  as  to  the  thermal  death  point  from  that  of  the  vege- 
tative hyphae.2  Nevertheless,  some  spores  of  even  parasitic  forms 
are  particularly  resistant.  It  would  appear  that  sclerotial-like  struc- 
tures or  similar  forms  are  also  capable  of  withstanding  high  tem- 
peratures, but  there  is  no  data  which  can  be  presented. 

Low  temperatures.  In  general,  fungi  are  able  to  withstand  very 
low  temperatures.  Few  fungous  spores  are  injured  at  o°  C.  It 
will  be  found  quite  generally  true  that  cultures  of  saprophytic  or 
parasitic  organisms  may  be  frozen  solid  in  freezing  mixtures  with- 
out unusual  injury.  The  effects  of  winter  conditions  are  not  ordi- 
narily such  as  to  destroy  fungous  spores  to  any  great  extent. 

Light.  The  ultimate  effect  of  light  of  different  intensities  upon 
organisms  may  be  manifest  through  injury,  change  of  form,  or 
special  stimulation.  The  immediate  cause  of  the  particular  in- 
fluence is  "always  difficult  to  determine,  as  is  true  in  cases  of  the 
action  of  most  external  agents.  A  considerable  number  of  in- 
vestigators have  studied  the  effects  of  light  upon  the  living  cells 
of  fungi  and  bacteria  with  regard  to  its  injurious  action,  inhibition, 
or  stimulation  of  germination,  and  the  effects  upon  growth  and 
reproductive  processes.  In  general  those  organisms  seem  most 
readily  injured  by  light  which  are  sensitive  to  many  other  exter- 
nal stimuli.  Pathogenic  bacteria  and  certain  hyaline  fungi  with 
specially  restricted  life  relations  are  soon  killed  by  direct  exposure 
to  sunlight.  Some  saprophytic  forms  are  more  resistant,  and  dark- 
colored  fungous  spores  or  hyphae  are  far  less  influenced.  Ward 
made  fresh  sowings  of  Bacillus  anthracis  in  nutrient  agar  in 
Petri  dishes,  covering  the  dishes  with  glass  or  quartz  plates,  and 

1  Duggar,  B.  M.    Bot.  Gaz.  27  :   131-136.    1899. 

2  O'Brien,  Abigail.    Built.  Torrey  Bot.  Club  29  :   170-172.    1900. 


72  PHYSIOLOGICAL  RELATIONS 

then  pasting  over  the  latter  a  black  paper  stencil.  After  an  ex- 
posure to  varying  durations  of  sunlight  or  to  the  electric  arc, 
the  dishes  were  placed  in  the  incubator.  The  resulting  colonies 
developing  show  that  an  exposure  of  six  hours  to  sunlight  is 
sufficient  to  sterilize  almost  completely  the  agar  in  those  areas  of 
the  dishes  to  which  sunlight  was  admitted,  corresponding  to  the 
stencil  mark.  He  also  threw  a  solar  spectrum  on  cultures  sim- 
ilarly made,  and  upon  incubation  it  was  demonstrated  that  the 
blue-violet  rays  are  most  injurious  in  their  action.  Since  this  kill- 
ing effect  is  not  evident  when  the  culture  is  exposed  in  a  vac- 
uum, it  would  seem  that  the  deleterious  action  is  probably  an 
oxidation  effect. 

It  may  perhaps  be  inferred  that  light  is  more  important  in  the 
destruction  of  the  spores  of  parasitic  fungi  than  are  all  other 
agencies  combined.  Nevertheless,  many  spores  are  well  pro- 
tected against  these  deleterious  effects.  However  this  may  be, 
a  large  number  of  fungous  spores  find  hiding  places  under  pro- 
tecting rifts  of  the  bark,  beneath  the  leaf  scales,  or  in  the  debris 
on  the  surface  of  the  soil,  so  that  an  adequate  proportion  survive 
the  resting  period,  as  a  rule,  to  continue  the  prevalence  of  all 
common  plant  diseases. 

Many  fungous  forms  are  wholly  independent  of  the  presence 
of  light  as  a  requisite  factor  in  normal  development.  On  the 
other  hand,  in  darkness  the  hymenophores  of  certain  species 
are  said  to  be  abnormal  in  form. 

The  results  indicate  that  light  has  an  injurious  and  retarding 
influence  on  the  germination  of  fungous  spores.  De  Bary  records 
that  certain  members  of  the  Peronosporaceae,  notably  Phytoph- 
thora  infestans,  germinate  with  difficulty  in  daylight  and  not  at 
all  in  sunlight,  and  Miss  Ferguson  and  others  have  confirmed 
this  observation  in  experiments  with  Agaricus  campestris  and 
many  other  Hymenomycetes.  Very  little  accurate  information 
is  at  hand  relative  to  the  effects  of  light  in  the  open  upon  the 
development  of  the  fruiting  stages  of  fungi. 

For  all  practical  purposes  in  culture  work  with  the  fungi,  the 
relation  of  light  is  not  generally  an  important  one.  The  studies 
which  have  been  made,  however,  should  be  followed  up  from  a 
quantitative  point  of  view,  for  the  exact  effects  of  light  intensities 


ENVIRONMENTAL  FACTORS  73 

or  quality  upon  form  and  color,  metabolism,  rate  of  growth,  etc., 
are  extremely  important  from  a  general  physiological  standpoint. 

Nutrients.  The  cultivation  of  fungi  upon  decoctions  or  in- 
fusions of  organic  substances,  or  upon  solid  organic  substrata, 
would  afford  only  through  a  tedious  process  of  comparative  study 
any  fundamental  ideas  of  fungous  nutrition.  The  ease  with  which 
fungi  may  be  grown  in  cultures  and  the  use  of  synthesized  culture 
media  have  afforded  an  opportunity  for  exact  determination  of  the 
elements  required  by  these  organisms.  There  may  be  some  specific 
variations,  but  it  is  now  generally  agreed  that  the  majority  of  the 
fungi  require  nine  elements,  viz.,  carbon,  hydrogen,  oxygen,  nitro- 
gen, sulfur,  phosphorus,  potassium,  magnesium,  and  iron. 

Carbon.  For  most  culturable  fungi,  whether  primarily  parasitic 
or  saprophytic,  carbon  is  available  as  grape  or  cane  sugar,  glycerin, 
asparagin,  peptone,  etc.,  in  fact,  in  almost  any  soluble  or  readily 
convertible  nontoxic  form.  It  is  to  be  inferred  that  the  obligate 
parasite,  as  well,  utilizes  the  soluble  carbohydrates,  peptones,  etc., 
of  the  host  cell,  but  its  exact  relations  cannot  well  be  determined. 
Owing  to  indirect  needs  in  respiration,  the  nutrient  solution  must, 
in  order  to  yield  a  considerable  growth  of  the  fungi,  contain  a 
relatively  large  proportion  of  carbohydrates. 

Nitrogen.  Nitrogen  may  be  furnished  to  the  readily  culturable 
fungi  in  the  form  of  nitrates  or  ammonia  compounds,  but  in  some 
cases  preferably  as  peptone,  casein,  or  in  other  organic  form.  It  is 
probable  that  the  adaptations  which  result  in  obligate  parasitism 
have  only  in  part  a  special  relation  to  the  nitrogen  food  supply. 
Some  fungi  may  be  cultivated  only  with  difficulty,  and  among  these 
forms  certain  species  are  benefited  by  using  as  a  substratum  por- 
tions of  the  natural  host  (steamed),  or  decoctions  prepared  from 
the  host  plant.  It  is,  however,  possible  that  this  relation  is  con- 
cerned with  special  stimuli,  and  has  no  bearing  on  the  nitrogen 
factor. 

The  relation  of  certain  parasitic  organisms  to  atmospheric  nitro- 
gen has  become  unusually  interesting.  It  has  been  shown  by  more 
than  one  observer  that  fixation  of  nitrogen  by  the  various  forms 
of  the  leguminous  tubercle  bacteria,  Pseudomonas  radicicola,  may 
proceed  in  suitable  artificial  cultures.  It  proceeds,  therefore,  with- 
out reference  to  symbiotic  association, 


74 


PHYSIOLOGICAL  RELATIONS 


Relatively  striking  results  have  been  obtained  by  Saida 1  with  the 
parasitic  fungus,  Phoma  Beta.  Some  data  from  cultures  seventy- 
five  days  old  with  50  cc.  of  media  are  as  follows  : 


PHOMA  BETVE 


Substances  added  to  a  nutrient  salt  solution  2 

Cane  sugar,  in 
grams 

Fixation  of  nitrogen, 
in  milligrams 

e 

.77Cn 

17 

I  18^8 

Cane  sugar  (+  (NH4)2CO3,  trace)     .... 

5 

I.I828 

Cane  sugar  (+  (NH4)2CO3,  trace)     .... 

10 

1.7742 

Cane  sugar  (+  (NH4)2CO8,  trace)  7*  -"  .  ,.-•&'• 

20 

3-5484 

Cane  sugar  (+  (NH4)2CO8,  trace)     .... 

30 

6.2097 

More  recently  Ternetz  3  has  isolated  five  endophytic  mycorhizal 
fungi  from  certain  Ericaceae,  all  of  which  have  been  found  to  be- 
long to  the  form  genus  Phoma.  Three  of  these  organisms,  viz., 
Phoma  radicis  Vaccinii,  Phoma  radicis  Oxycocci,  and  Phoma 
radicis  Andromeda,  have  shown  a  well-developed  capacity  for 
nitrogen  fixation  in  culture,  these  three  mentioned  working  even 
more  economically  than  Azotobacter  chroococcum,  the  amount  of 
nitrogen  fixation  in  milligrams  per  gram  of  dextrose  used,  being, 
under  the  conditions  of  culture,  respectively  22.14,  18.08,  10.92, 
and  10.66  for  the  four  organisms  mentioned.4 

The  mineral  nutrients  may  be  supplied  in  the  form  of  any  of  the 
soluble  salts,  the  neutral  salts  being,  in  general,  preferable.  Formulae 
for  culture  solutions  are,  however,  given  under  nutrient  media. 

1  Saida,  K.    Ueber  Assimilation  freien  Stickstoffes  durch  Schimmelpilze.  Ber. 
d.  deut.  hot.  Ges.  19:  (io7)-(ii5).    1901. 

2  This  solution  was  constituted  as  follows  : 

KH2P04 0.4 

Mgso4  ....:' 0.4 

CaCl2 trace 

Water .     .     100  cc. 

3  Ternetz,  Charlotte.   Ueber  die  Assimilation  des  atmospharischen  Stickstoffes 
durch  Pilze.   Jahr.  f.  wiss.  Bot.  44  :  353-408.    1907. 

4  Other  papers  of  interest  in  connection  with  the  fixation  of  nitrogen  by  fungi 
are  the  following : 

Puriewitsch,   K.    Ueber  Stickstoffassimilation  bei  den  Schimmelpilzen.    Ber.  d. 

deut.  bot.  Ges.  13:  342-345.    1895. 
Froehlich,  H.    Stickstoffbindung  durch  eiriige  auf  abgestorbenen  Pflanzen  haufige 

Hyphomyceten.   Jahr  f,  wiss,  Bot.  45  :  256-302.    1907. 


ENVIRONMENTAL  FACTORS 


75 


Solutions.  It  has  been  the  general  experience  that  the  readily 
culturable  parasitic  and  hemiparasitic  fungi  have  about  the  same 
relation  to  strengths  of  solu-  M  r 

tions  as  the  saprophytic  forms. 
Ordinarily,  therefore,  such 
forms  give  abundant  growth 
under  widely  different  condi- 
tions of  concentration  of  the 
substratum.  According  to 
Eschenhagen  the  concentra- 
tions at  which  Botrytis  cinerea 
may  grow  under  ordinary  cir- 
cumstances are  as  follows  : 
grape  sugar,  51  per  cent ; 
cane  sugar,  37  per  cent; 
sodium  nitrate  and  calcium 
chloride,  1 6  per  cent ;  sodium 
chloride,  1 2  per  cent.  In  the 
culture  work  in  the  laboratory 
it  will  be  found,  however,  that 
differences  in  the  strength  of  FIG.  15.  CELLS  OF  ERICACE/E  (after  Ter- 
the  culture  medium  will  be  netz),  AND  ORCHIDACE^E  WITH  ENDOPHYTIC 
accompanied  by  noticeable  MYC°RHIZA>  ALSO  CORALLOID  ROOTS 
differences  in  the  form  of  the  fungous  colony,  amount  of  the 
mycelium,  and  the  character  of  the  spores  produced. 


CHAPTER  V 

ARTIFICIAL  INFECTION 

Infection  experiments,  or,  as  usually  termed,  artificial  infection 
experiments,  are  essential  in  pathological  work.  They  may  be 
undertaken  for  a  variety  of  purposes,  among  which  the  most 
important  seem  to  be  the  following : 

1.  To  determine  if  a  given  organism  is  parasitic,  or  the  cause 
of  a  particular  disease. 

2.  To   determine  the  conditions  under  which  an  organism  is 
most  active  in  producing  a  disease,  as  well  as  the  natural  seat 
and  manner  of  infection. 

3.  To  determine  the  range  of  pathogenicity  of  a  given  organism  ; 
that  is,  to  demonstrate  what  varieties,  species,  genera,  etc.,  may  be 
considered,  potentially  at  least,  host  plants. 

4.  To  determine  the  relationship  of  the  different  stages  of  an 
organism  to  one  another  and  to  the  host,  or  hosts. 

5 .  To  determine  the  conditions  under  which  the  different  stages 
of  a  fungus  may  be  developed. 

6.  To  determine  the  special  relation  of  a  parasitic  organism  to 
lesions  or  abnormalities  of  the  host,  with  which  a  parasitic  organism 
may  be  constantly  associated. 

The  rules  of  proof  formulated  by  Koch,  especially  for  disease- 
producing  bacteria,  have  been  repeatedly  brought  before  investi- 
gators, yet  they  are  too  frequently  ignored.  They  are  appropriately 
termed  the  canons  of  Koch.  They  should  be  kept  in  mind  in  all 
pathological  work,  as  they  are  applicable  in  all  such  studies,  despite 
the  exceptions  which  may  sometimes  be  made.  These  rules  may 
be  expressed  as  follows  : 

a.  Under  diverse  conditions  the  fungus  must  be  constantly  and 
abundantly  associated  with  the  disease,  or  pathological  state. 

b.  The  organism  should  be  grown  in  pure  cultures,  when  pos- 
sible, and  its  differential  characteristics  well  studied. 

76 


ARTIFICIAL  INFECTION  77 

c.  The  characteristic  disease  should  be  produced  by  infection 
experiments  with  a  pure  culture. 

d.  The  fungus  associated  with  the  disease  induced  should  be 
identified  as  the  one  originally  separated, '  and  any  abnormalities  of 
host  should  likewise  correspond. 

The  purposes  of  the  infection  experiments  as  above  outlined 
are  merely  suggestive,  and  it  is  evident  that  a  single  series  of 
experiments  may  give  all  or  nearly  all  of  the  indications  desired. 
Each  subdivision,  however,  deserves  special  consideration. 

i.  With  such  obligate  parasites  as  the  Peronosporaceae,  Exoas- 
caceae,  Erysiphaceae,  Ustilaginales,  Uredinales,  and  some  others,  the 


FIG.  16.   CORRECT  USE  OF  BELL  GLASSES  IN  CERTAIN  TYPES  OF  INFECTION 
WORK.    (Photograph  by  Geo.  M.  Reed) 

constant  association  of  an  organism  with  a  diseased  condition  would 
usually  be  sufficient  to  denote  this  organism  as  the  cause  of  the 
disease.  The  conditions  required  for  spore  germination  are  in  many 
cases  unknown,  and  therefore  negative  results  would  be  of  no  great 
value.  There  is  therefore  a  two-sided  opportunity  for  study.  It 
would,  however,  be  absurd  to  say  that  Empusa  Muscce  is  not  the 
cause  of  the  well-known,  or  commonly  observed,  fly  disease.  Yet, 
so  far  as  the  writer  is  aware,  no  work  has  been  done  which  would 
be  counted  as  successful  in  the  artificial  propagation  of  such  dis- 
eases among  insects.  With  most  groups  of  fungi  and  with  the 
bacteria,  infection  experiments  must  be  made  if  the  work  in  hand 


78  PHYSIOLOGICAL  RELATIONS 

pretends  to  be  authoritative.  It  is  true  that  the  great  majority  of 
fungi  described  as  the  causes  of  plant  diseases  have  not  undergone 
experimental  tests,  although  it  will  be  admitted  by  most  experi- 
enced pathologists  that  a  large  proportion  of  the  claims  made  are 
just,  beyond  all  question.  Where  the  spore-bearing  parts  of  a 
fungus  emerge  directly  from  only  slightly  injured  tissues,  or  in 
other  equally  plausible  cases,  the  statement  of  parasitism  made  by 
an  experienced  pathologist  is  usually  correct.  In  all  cases  where 
decay  has  set  in,  or  where  there  is  great  discoloration  of  the  parts 
affected,  —  especially  in  root  and  stem  diseases,  leaf  spots,  leaf 
burns,  etc.,  —  experiments  are  necessary  to  determine  the  primary 
cause  of  the  disease. 

It  is  often  the  case  that  the  fruit  bodies  or  the  mycelial  stages 
of  several  different  fungi  are  found  associated  with  a  diseased  con- 
dition, and  it  is  necessary  to  determine  either  which  fungus  is  the 
real  cause  of  the  trouble,  or  what  part  each  one  may  play  in  the 
effect  produced.  All  organisms  must  be  isolated,  and  separate  in- 
fection experiments  should  be  made  with  each.  In  such  cases,  of 
course,  the  fungi  may  be  only  secondary,  appearing  more  as  sapro- 
phytes on  plants  which  are  diseased  owing  to  the  action  of  some 
more  general  environmental  factor,  to  the  injuries  of  some  insect, 
or  to  a  mechanical  agent.  In  many  instances  the  fruit  bodies  of  a 
causal  fungus  may  not  be  formed  until  after  the  death  of  the  plant, 
as  is  particularly  true  of  the  pyrenomycetous  fungi.  If.  not  readily 
developed  in  culture,  for  comparison  with  those  produced  in  nature, 
it  will  be  necessary  not  only  to  make  infection  experiments  with 
the  pure  cultures,  but  also  with  the  spores  produced  in  the  open. 
In  general,  controlled  infection  experiments  will  be  more  rigor- 
ously demanded  as  our  knowledge  is  advanced.  There  are  propor- 
tionally few  groups  of  fungi  which  may  be  designated  saprophytic 
or  parasitic  in  more  than  a  relative  sense. 

2.  Infection  experiments  often  enable  one  to  determine  the  role 
which  may  be  played  in  the  predisposition  to  attack  by  such  con- 
ditions as  excessive  moisture  in  the  atmosphere  or  soil,  the  state 
of  nutrition  of  the  host,  etc.  Excessive  moisture  in  the  soil  and 
the  crowding  together  of  seedlings  offer  advantageous  conditions 
for  the  outbreak  of  damping-off  diseases,  produced  by  such  fungi 
as  Rhizoctonia  and  Pythium.  Moisture  on  the  leaf  surfaces  favors 


ARTIFICIAL  INFECTION 


79 


the  spread  of  many  fungi  under  the  more  or  less  "forced  "  condi- 
tions of  the  greenhouses.  Overhead  watering  or  the  general  sprin- 
kling of  plants  is  sometimes  alone  sufficient  to  facilitate  greatly 
the  spread  of  disease,  as  in  the  case  of  the  rust  of  chrysanthemums. 
Unusual  succulence  in  the  pear  is  said  to  be  a  favorable  condition 
for  infection  by  the  pear  blight  organism.  In  general,  it  is  believed 
that  any  conditions  leading  to  the  suffusion  of  the  tissues  of  the 
host  with  water  invite  disease,  particularly  disease  accompanied  by 
the  general  destruction  of  the  tissues,  and  finally  by  decay. 

From  extended  observations  Atkinson  was  able  to  say  that  the 
absence  of  a  sufficient  amount  of  potash  in  the  soil  predisposes  the 
cotton  plant  to  the  attacks  of  Macrosporium  .nigricantium,  which 
fungus  is  then  the  cause  of  a  new  and  graver,  phase  of  the  disease. 
Many  analogous  cases  might  be  cited,  all  of  which  suggest  the 
necessity  of  experimental  work  from  the  standpoint  of  inoculation. 
Recently  Ward  has  reported  that  the  lack,  or  poverty,  of  one  or 
more  necessary  elements  in  the  nutrition  of  the  brome  grasses  does 
not  seem  to  predispose  those  hosts  to  the  rust  fungi  parasitic  upon 
them.  It  may  well  be  inquired  if  this  is  a  special  case,  and  particu- 
larly if  there  may  be  any  difference  in  this  regard  between  obligate 
and  facultative  parasites.  In  this  connection,  moreover,  the  experi- 
ments made  by  Salmon  with  Erysiphe  graminis  may  be  cited.  He 
found  that  a  wound  sometimes  sufficed  to  break  down  completely 
the  immunity  of  certain  species  of  grasses  to  a  particular  form,  or 
race,  of  this  fungus. 

The  method  of  penetration  of  the  germ  tube  of  the  fungus  can 
only  be  definitely  determined  by  careful  infection  experiments.  It 
is  just  as  true  for  a  fungous  disease  of  plants  as  for  a  bacterial  dis- 
ease that  a  thorough  study  of  the  conditions  has  not  been  made 
until  the  possible  methods  of  infection  are  determined.  Not  only 
is  it  necessary  in  the  general  etiology  of  the  Disease,  but  extremely 
important  in  the  formulation  of  preventive  measures.  Fungi  gain- 
ing entrance  only  through  injuries  or  wounds  are,  in  general,  much 
more  readily  suppressed  or  confined. 

3.  Inoculation  studies  with  certain  species  of  Glceosporium  have 
indicated  that  many  distinctly  disease-producing  organisms  may 
have  a  considerable  range  of  host  plants.  A  species  of  "Rhizoc- 
tonia  "  (Corticium  vagum  B.  &  C.,  var.  Solani  Burt)  causing  a 


8o  PHYSIOLOGICAL  RELATIONS 

rot  of  sugar  beets  may  cause  damping-off  diseases  of  seedlings,  as 
well  as  other  diseases,  in  several  different  families  of  hosts.  Of 
the  numerous  cases  which  might  be  cited  in  this  connection,  many 
are  in  need  of  critical  study,  notably  Exoascus.  Among  hemi- 
parasites,  or  facultative  parasites,  such  studies  will  doubtless  lead 
to  a  considerable  reduction  in  the  number  of  the  so-called  species 
of  such  fungi.  On  the  other  hand,  infection  experiments  have 
compelled  mycologists  to  break  up  among  others  the  old  species 
Puccinia  graminis  into  several  forms,  frequently  termed  biological 
or  physiological  forms,  or  subspecies,  which,  in  some  cases,  are 
entirely  indistinguishable  one  from  another  on  purely  morpho- 
logical grounds.  Each  form  has  a  restricted  number  of  host  plants, 
and  it  is  believed  that  no  cross  infections  occur.  Many  similar 
cases  have  been  clearly  demonstrated  for  the  Uredinales. 

It  has  recently  been  shown  that  certain  mildews,  notably  ErysipJic 
graminiS)  may  likewise  be  broken  up  into  forms  restricted  each  to 
one  or  more  jiost  plants.  The  two  fungi  mentioned  are  instances 
where  each  parasite,  as  a  species,  is  capable  of  infecting  a  large 
number  of  host  plants.  It  remains  to  be  seen  to  what  extent  such 
differentiation  of  forms  is  to  be  found  in  species  more  restricted 
as  to  host  plants. 

4.  Experimental  evidence  was  required  to  demonstrate  the  long- 
suspected  connection  between  Puccinia  graminis,  the  grain  rust, 
and  the  common  secidium  on  the  barberry,  SEcidium  Berberidis. 
Those  experiments,  although  preceded  by  studies  in  heteroecism 
upon  Gymnosporangium,  mark  a  very  distinct  epoch  in  infection 
work,  for  heteroecism  has  proven  a  very  important  biological  phe- 
nomenon. Within  the  past  few  years,  particularly,  much  has  been 
done  towards  a  systematic  endeavor  to  connect  by  experimental 
proof  the  heteroecious  forms  of  Uredinales.  Nevertheless,  much 
valuable  work  remains  to  be  done,  and  the  observant  student  will 
constantly  find  suggestions  in  the  proximity  of  host  plants  taken 
in  connection  with  the  sequence  of  stages  in  these  fungi.  It  is 
well  known  that  the  occurrence  of  a  uredo  or  teluto  stage  in  con- 
nection with  an  secidium,  or  closely  following  the  latter,  is  not  the 
final  proof  that  these  stages  are  connected.  A  close  observation  of 
many  affected  host  plants  during  different  seasons  may,  however, 
give  some  valuable  clews  as  to  relationships  and  prevent  fruitless 


ARTIFICIAL  INFECTION  8 1 

experimentation.  Finally,  in  this  it  is  again  to  be  urged  that  in  a 
study  of  the  relationship  of  stages  to  one  another  and  to  the  host 
plant,  by  artificial  infection,  experiments  should  be  made  upon 
properly  isolated  hosts. 

5.  In  some  regions  the  production  of  the  oospores  of  such  fungi 
as  Cyst  opus  candidus  and  Cystopiis  Bliti  are  practically  unknown  ; 
yet  in  other  regions,  and  during  certain  seasons,  the  oospores  are 
produced  in  great  abundance.    A  somewhat  similar  fact  is  the  con- 
tinuous production  of  conidia  by  some  species  of  Erysiphaceae  in 
certain  habitats.    Together  with  infection  experiments  under  differ- 
ent conditions,  and  upon  host  plants  of  various  ages,  physiological 
studies  of  the  host  will  be  required. 

6.  It  is  well  known  that  certain  Uredinales  and  Exoascaceae  are 
the  immediate  causes  of  the  witches'  brooms  of  the  hosts  in  con- 
nection with  which  these  fungi  are  found.    On  the  other  hand, 
SpJicerotheca  phytoptophila  grows  only  upon  branches  deformed  by 
phytoptids.    Fungi  are  associated  also  with   many  abnormalities 
commonly  referred  to  as  knots,  cankers,  etc.,  and  in  nearly  all  such 
cases  infection  experiments  should  be  called  into  service  to  deter- 
mine not  merely  if  the  fungus  is  parasitic,  but  also  to  determine 
if  it  is  the  primary  cause  of  the  abnormal  development.    Even  if 
the  fungus  is  known  to  be  parasitic,  from  the  point  of  view  of 
pathology,  the  fungus  becomes  a  matter  of  secondary  importance 
when  it  is  parasitic  merely  in  consequence  of  some  other  injury  or 
excitation. 

In  general,  infection  experiments  may  be  carried  out  either  in 
the  open  or  in  the  greenhouse.  Frequently  it  is  possible  to  study 
natural  infections.  Nevertheless,  adequate  opportunities  for  plant 
pathological  work  have  not  been  secured  until  a  good  greenhouse 
is  constantly  available. 

The  methods  of  making  inoculations  are  necessarily  various  but 
always  simple.  With  such  fungi  as  the  rusts,  mildews,  and  many 
species  producing  leaf  spots,  the  germ  tubes  usually  gain  entrance 
by  boring  through  the  epidermis  or  by  passing  in  at  the  stomata. 
No  injuries  or  abrasions  of  the  organs  inoculated  being  necessary, 
the  plant  may  be  moistened,  preferably  by  vigorous  spraying,  with 
distilled  water.  Bell  glasses  may  often  be  employed  if  ventilation 
is  provided  (Fig.  16).  In  some  cases  perfect  precautions  must  be 


82 


PHYSIOLOGICAL  RELATIONS 


taken  to  prevent  the  access  of  any  spores  from  other  sources. 
Ordinarily,  precaution  is  fairly  well  secured  by  a  sufficient  number 
of  control  plants. 

If  the  spores  of  a  given  fungus  are  obtainable  in  quantity,  these 
may  be  sprayed  on  the  plant  with  an  atomizer  or  small  pump.    A 

small  number  of  spores  may  be 
sponged  on  or  applied  with  a 
camel' s-hair  brush.  If  the  inoc- 
ulations are  made  towards  even- 
ing, and  the  plants  are  wrapped 
loosely  with  paper  or  cloth,  a 
moist  condition  may  be  readily 
maintained  for  a  period  suffi- 
ciently long.  The  cylindrical, 
open-topped,  glass,  insect  breed- 
ing-cage is  extremely  useful  as  a 
cover  for  inoculated  herbaceous 
plants  of  small  size  (Fig.  17). 
The  top  may  be  closed  with  a 
cloth,  and  thus  ventilation  is 
well  provided  for,  while  the 
moisture  retained  is  usually 
sufficient.  It  insures,  also,  pro- 
tection against  insects,  but  not 
against  wind-blown  spores.  Tall 
bell  glasses  may  be  used  when  an  atmosphere  practically  saturated 
is  not  objectionable.  In  this  case,  moreover,  a  relatively  favorable 
state  of  humidity  and  aeration  may  be  maintained  by  raising  the 
bell  glass  on  blocks.  To  provide  against  accidental  infection  great 
caution  must  be  observed,  as  stated  below.  In  the  local  inoculation 
of  a  twig,  glass  tubing  may  be  slipped  over  the  inoculated  branch  ; 
the  ends  of  the  tube  may  then  be  plugged  first  with  moist  and 
afterwards  dry  cotton.  Glass  vessels  so  employed  may  usually  be 
removed  within  a  few  days. 

Bacteria  and  certain  leaf  spot  and  stem  inhabiting  fungi  may 
require  wounding  of  the  surfaces  to  which  they  are  applied.  The 
wounds  may  be  made  either  with  sterile  needles,  scalpels,  or  scissors, 
and  the  depth  of  such  wounds  must  be  determined  by  experience 


FIG.  17.   INSECT  BREEDING-CAGE  IN 
INOCULATION  EXPERIMENTS 


ARTIFICIAL  INFECTION 


and  specific  needs.  In  particular  work  the  surface  thus  injured 
should  be  washed,  cleansed  with  a  disinfecting  solution,  if  the  struc- 
ture will  permit,  and  again  washed  with  distilled  water  before  the 
inoculation  is  made.  In  work  of  this  character  the  spores  or 
mycelium  for  inoculation  should  be  taken  from  a  pure  culture ; 
indeed,  pure  cultures  should  always  be  used  if  the  fungi  are  cul- 
turable,  except  where  the  only 
material  available  is  hopelessly 
mixed,  and  the  inoculation  is 
only  desired  to  eliminate  some 
of  the  saprophytic  forms.  It  is 
usually  well  to  cover  the  wounds 
with  grafting  wax  (Fig.  18),  or 
some  other  similar  adhesive  con- 
taining no  injurious  substance. 
This  will  be  possible  in  the  case 
of  stem  diseases.  In  this  case 
the  control  experiments  should 
be  wounded  and  covered  with 
wax  as  well,  so  that  the  condi- 
tions may  be  quite  the  same.  In 
some  instances  absorbent  cotton 
may  replace  the  wax. 

Whenever   the    air   may  too    Fia  l8'T  THE  UsE  OF  DRAFTING  WAX 

IN  INOCULATION  EXPERIMENTS 
readily  serve  as  a  source  of  con- 
tamination, plants  of  large  size  may  be  fairly  well  protected  from 
this  source  of  danger  by  using  practically  air-tight  glass  frames,  into 
which  the  air  may  enter  only  after  filtration  through  cotton,  and 
smaller  plants  may  be  accommodated  under  bell  glasses  with  open 
tops  loosely  plugged  with  cotton. 

Certain  disease  organisms  gain  entrance  through  the  roots,  as 
in  the  case  of  Neocosmospora  vasinfecta.  It  will  be  evident  in 
such  cases  that  the  soil  should  be  inoculated.  If  possible,  the  plants 
to  be  inoculated  should  be  grown  in  sterilized  soil,  but  another  con- 
sideration of  importance  frequently  is  to  have  the  soil  conditions 
imitate  as  closely  as  possible  the  conditions  under  which  the  disease 
was  developed  in  the  field  ;  thus  the  type  of  soil  and  the  percentage 
of  soil  moisture  are  important. 


84  PHYSIOLOGICAL  RELATIONS 

In  all  cases  inoculation  experiments  should  be  made  in  quantity, 
and  control  experiments  in  similar  number  must  be  relied  upon  to 
eliminate  any  possibility  of  error.  If  a  given  disease  is  particu- 
larly abundant  in  the  region,  and  accidental  infection  therefore 
more  probable,  the  number  of  control  cultures  should  be  further 
increased,  in  addition  to  the  special  precautions  mentioned. 

A  failure  to  secure  infection  from  a  relatively  small  number  of 
experiments  may  not  indicate  that  the  particular  fungus  plays  no 
part  in  the  production  of  the  disease  with  which  it  has  been  asso- 
ciated. At  any  rate,  experience  in  pathological  work  is  necessary 
when  one  assumes  to  make  a  positive  statement  in  this  regard.  In 
some  cases  infection  may  occur  at  a  definite  period  only,  or  closely 
related  species  of  fungi  may  differ  markedly  with  respect  to  the 
conditions  under  which  infection  may  take  place.  It  has  been 
found  that  the  fungus  causing  fruit  spot  of  apple  is  effective  at 
about  the  time  that  the  hairs  covering  the  surface  of  the  young 
apple  are  broken  off.  The  loose  smut  of  oats  penetrates  the  host 
only  when  the  latter  is  in  the  seedling  stage,  while  the  smut  of 
wheat  may  infect  the  blossom. 


CHAPTER  VI 

THE  PRINCIPLES  OF  DISEASE  CONTROL 

BAIN,  S.  M.    The  Action  of  Copper  on  Leaves  with  Special  Reference  to  the 

Injurious  Effects  of  Fungicides  on  Peach  Foliage.    Tenn.  Agl.  Exp.  Sta. 

Built.  (Vol.)  15  :  21-108.  pis.  1-8.    1902. 
BURT,  E.  A.    Resistance  of  Plants  to  Parasitic  Fungi.    Trans.  Mass.  Hort. 

Soc.  (1898):   145-161. 
CLARK,  J.  F.    On  the  Toxic  Properties  of  Some  Copper  Compounds  with 

Special  Reference  to  Bordeaux  Mixture.    Botan.  Gaz.  33  :   26-48.  Jigs. 

7-7.    1902. 
HEDRICK,  U.  P.    Bordeaux  Injury.    N.  Y.  Agl.  Exp.  Sta.  Built.  287:   1-189. 

1907. 
JACKSON,  H.  S.  Development  of  Disease  Resistant  Varieties  of  Plants.    Trans. 

Mass.  Hort.  Soc.  (1908):   123-137. 

LODEMAN,  E.  G.    The  Spraying  of  Plants.    399  pp.    92  figs.    1896. 
MILLARDET,  A.   De  Faction  des  melanges  de  sulfate  de  cuivre  et  de  chaux  sur 

le  mildion.    Compt.  Rend.  101 :  929-932.    1885. 
SCOTT,  W.  M.    Self-Boiled  Lime-Sulphur  Mixture  as  a  Promising  Fungicide. 

Bureau  Plant  Industry,  U.  S.  Dept.  Agl.  Circular  1  :    1-18.  figs.  /,  2. 
(Spray  Calendars  and  Bulletins  of  the  Agl.  Exp.  Sta.'s  in  the  United  States.) 
SWINGLE,  W.  T.    Bordeaux  Mixture.    Div.  Veg.  Phys.  and  Path.,  U.  S.  Dept. 

Agl.  Built.  9:    1-37.    1896. 

I.    METHODS    OF    CONTROL 

A  proper  knowledge  of  the  life  histories  of  parasitic  fungi,  ex- 
perience in  the  use  of  spray  mixtures,  an  adequate  conception  of 
crop  requirements,  and  a  comprehension  of  general  plant  physiol- 
ogy make  possible  in  the  great  majority  of  cases  a  rational  means 
of  disease  control. 

Eradication,  prevention,  or  control  of  fungous  diseases  may  be 
brought  about  more  or  less  successfully  by  proper  regard  for  such 
factors  as  varietal  resistance,  seed  selection,  crop  rotation,  seed 
treatment,  application  of  fungicides  to  the  growing  crop,  and  gen- 
eral sanitation.  It  is  frequently  necessary  to  combine  several  methods 
of  procedure  in  combating  the  attacks  of  a  single  organism,  and 
in  no  case  should  practices  of  general  sanitation  be  disregarded. 

Resistant  varieties.  Notable  instances  of  the  resistance  of  par- 
ticular varieties  of  important  parasitic  fungi  have  been  brought  to 

85 


86  PHYSIOLOGICAL  RELATIONS 

the  attention  of  growers  and  pathologists  from  early  times.  It  is, 
in  fact,  seldom  that  all  the  individuals  of  even  a  well-established 
variety  are  equally  susceptible  to  disease,  arid  the  differences  be- 
tween closely  related  varieties  are  often  surprisingly  great.  The 
Iron  cowpea  has  been  shown  to  be  far  more  resistant  than  other 
varieties  to  the  wilt  disease,  and  a  new  strain  of  cotton,  the  Dillon, 
possesses  similar  qualities  with  respect  to  the  same  fungus.  Every 
carnation  grower  became  familiar  a  few  years  ago  with  the  fact  that 
the  Scott  carnation  was  peculiarly  susceptible  to  carnation  rust,  and 
that  under  ordinary  conditions  the  Enchantress  was  peculiarly  re- 
sistant. The  Kieffer  pear  is  far  less  attacked  by  blight  and  leaf 
spot  fungi  than  other  varieties  commonly  grown.  Nearly  all  fruits, 
vegetables,  field  crops,  and  floricultural  plants  will,  upon  careful 
investigation,  give  evidence  of  more  or  less  striking  qualities  of  re- 
sistance. This  resistance  may  be  inherited,  or  it  may  be  a  charac- 
teristic which  changes  markedly  as  the  climatic  or  soil  conditions 
vary  under  which  the  host  plant  may  be  growing.  The  relations 
to  disease  may,  therefore,  be  complex,  and  it  is  not  the  purpose  of 
this  summary  account  of  disease  control  to  describe  at  length  the 
diverse  relations  of  host  and  parasite. 

Seed  selection.  Seed  selection  is,  in  many  cases,  the  easiest 
and  most  natural  method  of  disease  control.  The  anthracnose  of 
beans  is  carried  over  from  crop  to  crop  very  largely  by  means  of 
diseased  seed,  and  it  has  been  shown  that  diseased  pods  mean  as 
a  rule  diseased  seed,  that  treatment  of  such  diseased  seed  is  not 
effective,  and  that,  therefore,  the  most  rational  method  of  combat- 
ing the  organism  is  to  plant  seed  from  selected  pods.  It  is  very 
probable  that  the  anthracnose  of  cotton  is  similarly  transferred 
from  year  to  year.  Certainly  the  appearance  of  the  anthracnose 
abundantly  upon  the  seedlings,  especially  upon  the  cotton  leaves, 
suggests  the  presence  of  the  organism  in  the  seed.  The  late  blight 
of  potato  seems  to  be  commonly,  if  not  entirely,  carried  over  from 
season  to  season  by  means  of  diseased  tubers,  the  latter  being  in- 
fected with  a  form  of  the  disease  known  as  the  potato  rot.  The 
selection  of  seed  from  a  field  in  which  no  blight  has  been  present 
to  a  very  large  extent  insures  a  crop  free  from  blight.  Seed  selec- 
tion is  already  practiced  to  a  considerable  extent,  but  there  is  no 
line  of  disease  control  requiring  more  attention  at  the  present  time. 


THE  PRINCIPLES  OF  DISEASE  CONTROL  87 

Crop  rotation.  There  is  no  small  number  of  fungous  diseases 
which  reappear  year  after  year  on  account  of  the  fact  that  the  soil 
has  become  contaminated  with  the  spores  or  mycelium  of  the  fun- 
gus, these  stages  being  often  able  to  remain  alive  throughout  a 
considerable  period  of  time.  It  is  only  possible  to  prevent  many 
of  these  diseases  by  the  practice  of  a  suitable  rotation.  Land 
infested  with  the  organism  causing  club  root  of  cabbage  and  tur- 
nips should  be  kept  free  from  cruciferous  plants  for  two  years. 
The  fungus  producing  scab  of  potatoes  is  far  more  persistent  in 
the  soil  than  the  last  mentioned  ;  and  Urocystis  Cepulcz,  the  onion- 
smut  organism,  is  supposedly  able  to  retain  the  capacity  for  ger- 
mination in  the  soil  for  a  number  of  years.  In  addition,  there  are 
many  other  fungous,  as  well  as  bacterial,  diseases  for  which  it  is 
essential  to  practice  the  strictest  rotation  principles. 

The  application  of  fungicides.  The  application  of  fungicides  to 
the  growing  crop  has  been  for  about  twenty  years  a  principal  means 
of  disease  control  or  prevention.  In  this  connection  it  is  under- 
stood that  the  application  of  a  fungicide  to  the  host  plant  is  gener- 
ally for  the  purpose  of  protecting  it  from  an  attack  of  a  fungus. 
In  only  a  few  cases  is  it  possible  to  actually  kill  an  organism  which 
is  already  causing  injury.  In  the  case  of  some  of  the  powdery  mil- 
dews the  use  of  any  fungicidal  sprays  or  dusts  may  be  beneficial, 
in  part,  from  the  direct  killing  action  of  the  fungicide  upon  the 
superficial  growth  of  the  fungus.  In  the  great  majority  of  instances 
the  fungicide  is  applied  with  the  view  of  covering  a  healthy  plant, 
which  is  thus  to  be  kept  in  healthy  condition.  The  germination  of 
the  fungous  spore,  which  may  follow  upon  the  host  subsequent  to  the 
application  of  the  fungicide,  should  thus  be  prevented.  It  has  been 
fairly  well  demonstrated  that  the  germinating  spore  will,  for  in- 
stance, absorb  from  the  nearly  insoluble  copper  compounds  of 
Bordeaux  mixture  sufficient  toxic  substances  to  cause  its  death. 

At  the  same  time,  it  is,  of  course,  necessary  that  the  fungicides 
shall  be  of  a  nature  and  strength  which  will  be  in  general  nonin- 
jurious  to  the  plant  which  is  to  be  protected.  It  is  not,  however, 
possible  to  determine  this  point  precisely,  since  apparently  under 
different  climatic  conditions  the  injurious  action  of  the  fungicide 
may  vary  greatly.  Weak  Bordeaux  mixture  will  be  noninjurious  to 
the  foliage  of  peach  and  plum,  or  even  to  apple,  one  season  and 


88  PHYSIOLOGICAL  RELATIONS 

the  following  year  applied  with  equal  care  the  same  mixture  will 
cause  great  injury  or  defoliation.  Moreover,  since  the  various  para- 
sitic fungi  are  differently  affected  by  the  strength  as  well  as  the 
composition  of  the  fungicide,  it  is  important  to  know  the  specific 
relations  of  each  important  parasitic  organism.  In  the  use  of  fun- 
gicides there  is  a  very  large  field  of  investigation  possible  because 
of  the  fact  that  an  intimate  knowledge  of  the  life  histories  of  the 
organisms  concerned  alone  affords  a  proper  index  of  the  best  time 
for  the  application  of  the  mixture,  climatic  conditions,  and  innu- 
merable other  factors,  serving  also  to  modify  the  requirements  in 
special  cases.  It  has  been  possible  to  control  very  satisfactorily  the 
blight  fungi  of  potato,  most  of  the  commoner  grape  parasites,  the 
bitter  rot  and  scab  of  the  apple,  as  well  as  numerous  other  diseases 
by  proper  use  of  Bordeaux  mixture.  Nevertheless,  Bordeaux  mix- 
ture should  not  be  relied  upon  to  the  exclusion  of  other  fungicides, 
nor  is  the  indiscriminate  use  of  any  fungicide  to  be  generally 
recommended. 

II.  PREPARATION   OF   FUNGICIDES 

The  more  commonly  employed  of  the  many  fungicides,  which 
have  been  used  by  practical  growers  and  plant  pathologists,  are 
as  follows  :  Bordeaux  mixture,  ammoniacal  copper  carbonate,  lime- 
sulfur  wash,  potassium  sulfide,  flowers  of  sulfur,  copper  sulfate, 
corrosive  sublimate,  and  formalin.  Of  these  preparations  the 
first  five  may  be  employed  upon  the  foliage  during  the  growing 
condition  of  the  plants.  The  remaining  substances  are  generally 
used  for  disinfection  of  seeds  and  plants  in  dormant  or  winter 
condition. 

Bordeaux  mixture.  Bordeaux  mixture  is  the  most  important 
and  the  most  commonly  employed  of  fungicides.  As  a  rule  it 
is  true  that  Bordeaux  mixture  will  protect  a  plant  from  fungous 
attack  where  it  is  possible  to  protect  it  by  means  of  any  spray 
mixture.  Its  injurious  effects  upon  some  plants  preclude  its 
use.  In  other  cases  the  discoloration  of  fruits  immediately  before 
marketing  would  render  them  less  desirable  for  market  purposes, 
and  again  the  discoloration  of  the  foliage  makes  it  objectionable 
in  the  case  of  ornamental  plants.  Bordeaux  mixture  may  be  used 
also  for  plants  in  dormant  condition,  Under  such  circumstances 


THE  PRINCIPLES  OF  DISEASE  CONTROL  89 

very  strong  solutions  may  be  employed.  The  strength  of  solu- 
tion now  generally  regarded  as  a  standard  consists  of : 

Copper  sulfate 5  lb. 

Stone  lime i   •  .^    .       5  lb. 

Water .'';•  «  •    :*  .  .-.     5°  gal. 

A  mixture  of  this  strength  is  known  as  the  5-5-50  formula. 
The  strength  may  be  decreased  or  increased  as  desired,  and  it  will 
be  expressed  in  a  similar  manner,  thus  2-2-50  and  10-10-50 
respectively  refer  to  2  pounds  of  each  chemical  and  to  10  pounds 
of  each  in  50  gallons  of  water.  The  method  of  making  Bordeaux 
consists  in  dissolving  the  required  amount  of  copper  sulfate  in 
an  equal  number  of  gallons  of  water,  the  copper  sulfate  being 
placed  in  a  sack  and  suspended  in  a  barrel  or  other  vessel,  this 
method  greatly  facilitating  the  solution. 

The  amount  of  lime  required  may  be  slowly  slaked  in  another 
barrel  or  vessel  and  then  brought  up  to  a  thick  milk  with  a  known 
quantity  of  water.  This  solution  may  be  used  as  a  stock  solution, 
i  gallon  of  the  copper  sulfate  representing  i  pound  of  the  copper 
salt,  and  i  gallon  of  the  lime  milk  representing  i  pound  or  more 
according  as  the  mixture  has  been  prepared.  The  amount  of  the 
copper  solution  for  a  barrel  or  tank  may  then  be  diluted  practically 
to  the  capacity  of  the  vessel  employed,  and  then  the  fairly  diluted 
lime  milk  is  poured  in,  stirring  constantly.  It  is  desirable  that  the 
latter  should  be  strained.  The  strong  stock  solutions  should  not 
be  poured  together. 

Ammoniacal  copper  carbonate.  This  preparation  is  frequently 
employed  where  a  strong  fungicide  is  needed,  and  where  the 
color  of  the  Bordeaux  mixture  renders  it  objectionable,  the  am- 
moniacal  solution  discoloring  foliage  to  only  a  very  slight  extent. 
The  constituents  of  this  mixture  are  as  follows  : 

Copper  carbonate 5  oz. 

Ammonia  (26°  Baume') 3  pt. 

Water 50  gal. 

The  strong  ammonia,  which  one  must  handle  carefully,  may  be 
diluted  to  about  five  times  its  volume,  and  the  copper  carbonate 
may  be  rubbed  up  with  water  in  a  small  vessel  to  form  a  thin 
paste.  This  paste  is  added  to  the  now  dilute  ammonia  with 


9o 


PHYSIOLOGICAL  RELATIONS 


constant  stirring.  The  mixture  is  then  brought  up  to  50  gallons. 
Ammoniacal  copper  carbonate  should  be  used  as  promptly  as 
possible,  owing  to  the  rapid  evaporation  of  the  ammonia. 

Lime-sulfur  wash.  The  lime-sulfur  preparation  which  may  be 
employed  with  least  fear  of  injury  to  growing  plants  is  a  form 
known  as  "  self -cooked."  It  has  been  introduced  relatively  re- 
cently, and,  therefore,  has  not  been  extensively  employed  by  com- 
mercial growers.  The  constituents  are  as  follows  : 

Flowers  of  sulfur 10  Ib. 

Stone  lime 10  Ib. 

Water 50  gal. 

The  preparation  of  the  mixture  is  simple.  After  weighing  the 
lime  into  a  barrel  add  three  gallons  of  water,  sift  in  the  sulfur, 
and  slake  the  lime  slowly.  As  heating  proceeds  add  more  water 
and  stir  occasionally.  The  heat  developed  is  sufficient  to  "  cook  " 
to  the  extent  desired.  When  completely  slaked  cool  promptly  by 
diluting  to  fifty  gallons.  Patent  preparations  are  made. 

Potassium  sulfide.  Potassium  sulfide  is  a  fungicide  which  is 
also  employed  when  it  is  undesirable  to  have  foliage  discolored. 
It  is,  moreover,  believed  to  be  especially  effective  in  the  preven- 
tion of  certain  mildews,  especially  that  of  the  gooseberry,  and 
also  the  rust  of  carnations.  This  substance  is  sometimes  known 
as  liver  of  sulfur,  and  should,  when  fresh,  make  a  solution 
yellowish  brown.  It  is  employed  in  the  following  preparation : 

Potassium  sulfide 3-5  oz. 

Water .       10  gal. 

Sulfur.  Flowers  of  sulfur  is  often  surprisingly  effective  in  the 
treatment  of  certain  surface  mildews,  such  as  that  of  the  rose. 
It  may  be  dusted  over  the  plants  so  as  to  fairly  cover  them  with 
the  yellow  powder,  and  is  particularly  effective  when  the  plants 
are  wet.  A  paste  of  sulfur  and  lime  is  also  employed  by  many 
growers  in  rose  houses,  the  method  of  application  being  then  to 
smear  the  steam  pipes  with  the  mixture,  the  fumes  from  which 
are  disastrous  to  the  mildew. 

Recently  a  sulfufic  acid  solution  of  a  strength  of  i-iooo  has 
also  been  successfully  employed  in  the  treatment  of  rose  mildew 
and  similar  fungi. 


THE  PRINCIPLES  OF  DISEASE  CONTROL  91 

Copper  sulfate.  Copper  sulfate  is  frequently  employed  as  a 
wash  for  dormant  trees  and  also  for  disinfecting  seed  of  grains 
which  may  be  contaminated  by  adherent  fungous  spores.  The 
solution  may  be  prepared  as  suggested  under  Bordeaux  mixture. 
When  diluted,  it  should  consist  of : 

Copper  sulfate I  Ib. 

Water v-:  . ''•":.     15  gal. 

It  is  seldom  that  one  would  desire  to  apply  copper  sulfate 
to  the  growing  tree,  on  account  of  its  injurious  action  upon  the 
leaves,  but  occasionally  it  has  been  employed  at  a  strength  of 
i  pound  to  100  gallons  of  water. 

Corrosive  sublimate.  Bichloride  of  mercury,  commonly  known 
as  corrosive  sublimate,  is  an  unusually  strong  poison  for  man  as 
well  as  for  animals ;  at  the  same  time  it  is  a  very  effective  disin- 
fectant and  is  very  generally  employed  for  potato  scab.  The 
solution  consists  of : 

Corrosive  sublimate 2  oz. 

Water  .     .     .  '  s     ,     ....     .     .     15  gal. 

This  is  practically  a  solution  of  i-iooo  by  weight,  a  strength  com- 
monly employed  by  physicians  for  disinfecting  purposes.  Seed 
potatoes  which  may  have  come  in  contact  with  the  scab  fungus 
should  be  soaked  for  one  and  a  half  hours  in  a  solution  of  the 
strength  indicated.  This  solution  may  also  be  used  as  an  anti- 
septic dressing  for  wounds,  especially  after  pruning.  It  should  be 
made  in  a  wooden  or  earthenware  vessel,  since  it  attacks  metallic 
substances  vigorously. 

Formalin.  Formaldehyde  vapor  dissolved  in  water  to  give  a 
solution  which  is  ordinarily  40  per  cent  bears  generally  the  com- 
mercial name  formalin.  It  is  like  the  last-mentioned  fungicide, 
also  a  strong  disinfectant,  and  is  used  very  extensively  for  treating 
seed  potatoes  and  seed  oats  and  wheat.  It  should  be  employed  of 
the  following  strength  : 

Formalin i  oz. 

Water 2  gal. 

Since  formalin  is  a  chemical  which  may  be  handled  more  con- 
veniently and  with  less  danger  than  corrosive  sublimate,  it  must  be 
given  the  preference. 


92  PHYSIOLOGICAL  RELATIONS 

Precautionary  measures.  Among  the  fungicides  discussed  arsen- 
ical poisons  have  not  been  included  for  the  reason  that  they  are 
supposed  to  be  of  importance  only  in  the  control  of  insect  pests. 
Frequently  it  becomes  desirable  to  combine  an  arsenical  compound 
-  Paris  green,  for  instance  —  with  Bordeaux  mixture,  and  thus 
accomplish  a  double  purpose.  In  that  case  more  than  a  pound  of 
lime,  additional,  should  be  included  in  the  Bordeaux  for  each 
pound  of  the  Paris  green  employed,  otherwise  injury  may  result. 

The  lime-sulfur  mixtures  are  now  receiving  attention  through- 
out the  country,  and  there  are  indications  that  they  may  become 
important.  Experiments  thus  far  show  that  the  ordinary  lime-sul- 
fur wash  is  much  more  toxic  to  sensitive  foliage  than  the  "  self 
cooked."  Growers  should  therefore  clearly  distinguish  between 
these  preparations.  Moreover,  the  ordinary  lime-sulfur  is  a  kind 
of  whitewash,  and  if  employed  when  the  fruit  is  approaching 
maturity,  it  may  be  objectionable  in  marketing. 


PART  III 

FUNGOUS  DISEASES  OF  PLANTS 

CHAPTER  VII 

GENERAL  CLASSIFICATION 
I.    FUNGOUS  DISEASES  AND  PATHOLOGY 

COMES,  D.  O.    Crittogamia  agraria.    600  pp.    17  pis.    1891. 

FRANK,  A.  B.    Die  Krankheiten  der  Pflanzen    (Pilzparasitaren  Krankheiten) 

2:  574  pp.    95  figs-    l896-    Breslau. 
FREEMAN,  E.  M.    Minnesota  Plant  Diseases  (Report  of  the  Survey,  Bot.  Series 

V).    432  pp.    211  figs.    1905.    St.  Paul. 
HARTIG,   R.     Lehrbuch  der  Baumkrankheiten.     3d  ed.     324  pp.     250  figs. 

1900.    Berlin,    (zd  ed.  transl.  into  English  by  Somerville  and  Marshall 

Ward.    331  pp.    159  figs.    1894.) 

KUHN,  J.    Krankheiten  der  Kulturgewachse.    312  pp.    7  pis.    1858.    Berlin. 
MASSEE,  G.    Text-book  of  Plant  Diseases.    458  pp.    92  figs.    1896. 
PRILLIEUX,  ED.    Maladies  des  plantes  agricoles  et  des  arbres  fruitiers  et  fores- 
tiers  cause'es  par  des  parasites  vege'taux  1 :  421  pp.  190  figs,  j  2  :  592  pp. 

figs.  191-484. 

SMITH,  W.  G.    Diseases  of  Field  and  Garden  Crops.    353  pp.   143  figs.    1884. 
SORAUER,  P.    Pflanzenkrankheiten  2  :  (2d  ed.)  456  pp.  iSpls.  21  figs.   1889. 

Berlin.    (3d  ed.  revised  by  Lindau.    562  pp.    62  figs.    1908.) 
TUBEUF,  K.  VON,  and  SMITH,  W.  G.    Diseases  of  Plants  induced  by  Crypto- 

gamic  Parasites.    598  pp.  330  figs.    1897. 
UNGER,  F.    Die  Exanthema  der  Pflanzen  und  einige  mit  diesen  verwandte 

Krankheiten  der  Gewachse.    422  pp.    7  pis.    1833. 
WARD,  H.  MARSHALL.    Timber  and  Some  of  its  Diseases.    295  pp.   45  figs. 

1889. 
WARD,  H.  MARSHALL.    Diseases  in  Plants.    309  pp.    1901. 

If  we  interpret  disease  as  any  apparently  abnormal  condition  of 
an  organism  or  of  its  parts  or  functions,  it  is  evident  that  the 
diseases  of  plants,  like  those  of  other  living  things,  include  mor- 
phological and  physiological  disturbances  which  may  be  induced 
by  a  variety  of  environmental  factors,  living  or  nonliving.  The 
popular  conception  excludes  from  the  category  of  plant  diseases 
those  effects  caused  by  predatory  animals  or  by  sudden  mechanical 

93 


94 


FUNGOUS  DISEASES  OF  PLANTS 


means.  There  is  also  a  tendency  to  dissociate  from  plant  diseases 
proper  the  widespread  devastation  which  is  the  result  of  the  varied 
injuries  annually  inflicted  by  insects.  In  general,  therefore,  we 
may  disregard  insects  as  the  cause  of  plant  diseases  when  that 
term  is  applied  narrowly. 

It  is  within  comparatively  recent  times  that  the  specific  injuries 
or  modifications  of  climatic  or  other  physical  factors  of  the  envi- 
ronment have  been  carefully  studied.  When  properly  understood, 
these  effects  have  moreover  frequently  been  termed  "  physiolo- 
gical "  as  opposed  to  "  pathological."  With  a  broad  definition  of 
pathological  this  interpretation  would  be  illogical.  Nevertheless 
the  student  of  fungous  diseases  of  plants  has  been  the  chief  plant 
pathologist.  This  is  partially  due  to  the  fact  that  the  disease-pro- 
ducing fungi  are  'intimately  associated  with  the  structure  of  plants, 
and  a  proper  study  of  the  fungus  has  necessitated  a  thorough  com- 
prehension of  its  relation  to  the  plant  upon  which  it  grows,  the 
host.  Plant  diseases  and  plant  pathology  are,  therefore,  more  or 
less  synonymous  with  fungous  diseases  of  plants,  and  the  narrow 
use  of  the  term  plant  pathology  will  on  this  account  doubtless 
long  persist. 

II.    THE  CLASSES  OF  FUNGI 

CORDA,  A.  C.  I.    Icones  Fungorum.   (In  6  parts,  large  4to.)  366  pp.   64  pis. 

1837-1857. 
ELLIS,  J.  B.,  and  EVERHART,  B.  M.   North  American  Pyrenomycetes.   793  pp. 

31  pis.    1892. 
ENGLER  and  PRANTL  (Eds.).  Die  natiirlichen  Pflanzenfamilien  1  (i*) :  570  pp. 

263  figs.;  1(1**):   513  pp.    293  figs. 
FARLOW,  W.  G.,  and  SEYMOUR,  A.  B.  A  Provisional  Host  Index  of  the  Fungi 

of  the  United  States.    219  pp.    1888-1891. 

SACCARDO,  P.    Sylloge  Fungorum.    (18  vols.  to  date.)    1882-1906. 
SCHROETER,  J.    Die  Pilze  (Cohn's  Kryptogamen  Flora  von  Schlesien),  Pt.  1: 

814  pp.;   Pt.  2:   500  pp.    1869. 
WINTER,  G.    Die  Pilze   (Rabenhorst's   Kryptogamen    Flora),  Vol.  1  (Pt.  i): 

924  pp.    111.;  Vol.  1  (Pt.  2):  928  pp.   111. 

BREFELD,  O.    Untersuchungen   aus   dem   Gesammtgebiete  der    Mykologie. 

(Extensive;  in  13  parts;  illustrated.)    1872-1905. 

COOK.E,  M.  C.  Introduction  to  the  Study  of  the  Fungi.  360  pp.  148 figs.  1895. 
DE  BARY,  A.  (Transl.  into  English  by  Garnsey  and  Balfour.)  Comparative 

Morphology  and  Biology  of  the  Fungi,  Mycetozoa,  and  Bacteria.    525  pp. 

198  figs.    1887. 
LAFAR,  FR.  (Ed.).   Handbuch  der  technischen  Mykologie.   (In  5  vols.;  4  vols. 

complete  to  date.)    1:   749  pp.    2 pis.    95  figs.;    2:   503  pp.    IQ pis.    90 

figs.;    3:  573  PP-  37  figs,  j    4:  558  pp.    122  figs.    1904-. 


GENERAL  CLASSIFICATION 


95 


TAVEL,  F.  VON.  Vergleichende  Morphologic  der  Pilze.   208  pp.  90  Jigs.   1892. 
TULASNE,  L.  R.  et  C.     Selecta  Fungorum  Carpologia.    (In  3  vols.)    782  pp. 

64pls.    1861-1865. 

UNDERWOOD,  L.  M.   Molds,  Mildews,  and  Mushrooms.   214  pp.  9  pis.    1899. 
ZOPF,  W.    Die  Pilze.    500  pp.    163  figs.    1898. 

Every  great  division,  or  class,  of  the  fungi  contains  some  spe- 
cies capable  of  producing  disease  in  other  plants.  Disease,  in  this 
connection,  refers  to  a  physiological  disturbance,  often  accom- 
panied by  anatomical  injuries  or  hypertrophies.  The  number  of 
such  disease-producing  organisms  is  sometimes  very  limited  in  a 
class,  and  there  are  orders  in  which  no  such  organisms  have  been 
described. 

In  a  restricted  sense  the  fungi  may  include  only  certain  classes 
of  chlorophyll-free  thallophytes,  but  in  the  broader  application  of 
the  term,  it  includes  all  chlorophyll-free  organisms  which  may  be 
regarded  as  plants.  It  is  with  this  latter  meaning  that  the  term  is 
here  used,  in  so  far  as  the  general  selection  and  arrangement  of 
material  is  concerned,  although  this  will  not  be  permitted  to  affect 
the  use  of  the  word  in  a  restricted  sense  as  well.  The  fungi  in- 
clude five  well-marked  classes  of  organisms,  as  follows. : 

1.  Myxomycetes.    The  slime  molds. 

2.  Schizomycetes.    The  bacteria. 

3.  Phycomycetes.    Water  molds,  black  molds,  downy  mildews, 
etc.,  —  algal-like  fungi. 

4.  Ascomycetes.    The  ascus-bearing  fungi. 

5.  Basidiomycetes.  Basidia-bearing  fungi, — smuts,  rusts,  mush- 
rooms, etc. 

This  grouping,  however,  shall  not  be  taken  to  indicate  a  line  of 
development  beginning  with  the  slime  molds  and  advancing  through 
the  other  groups  to  the  smut  and  mushroom  class.  In  fact,  only 
the  Phycomycetes,  Ascomycetes,  and  Basidiomycetes,  which  have 
much  in  common,  may  be  regarded  as  the  true  fungi,  and  nearly 
all  the  species  here  included  have  a  filamentous  vegetative  stage. 
The  bacteria  form  a  coherent,  distinct  class,  yet  certain  families 
show  very  close  relationship  with  the  fungi,  while  others  show  more 
striking  resemblances  to  certain  families  of  algae.  The  bacteria 
have,  moreover,  in  no  sense  any  very  close  animal-like  allies.  The 
Myxomycetes  have  no  very  apparent  relationship  with  any  other 


98 


FUNGOUS  DISEASES  OF  PLANTS 


Woronin  estimated  the  losses  due  to  it  in  the  vicinity  of  St.  Peters- 
burg at  $225,000.  In  the  United  States  it  has  been  disastrous  in 
many  of  the  northeastern  states,  particularly  in  those  trucking 
regions  which  supply  the  markets  of  New  York  and  Boston. 

It  is,  however,  occasionally 
found  both  South  and  West. 
The  limits  of  its  distribution 
have  not  been  clearly  denned. 
Unquestionably  it  thrives  best 
in  a  rich,  warm,  moisture- 
retaining  soil. 

Seedling  plants  affected  by 
this  parasite  show  a  decided 
' '  flagging. ' '  They  are  stunted, 
unhealthy  in  appearance,  and 
they  may  gradually  die.  Few 
of  those  affected  when  young 
reach  maturity.  The  parasite 
attacks  the  roots  and  gains 
entrance  to  the  parenchym- 
atous  tissues.  The  presence  of 
the  organism  within  the  cells 
affords  a  stimulus  to  abnormal 
growth.  There  results,  in 
fact,  malformities  of  striking 
appearance.  These  vary,  on 
the  one  hand,  from  slight 
nodose  swellings  in  the  small 
rootlets,  and  knotty  masses  in 
the  tough  roots  of  some  weeds, 
to  the  more  or  less  irregular, 
but  generally  fusiform,  digitate  swellings  (Fig.  19)  in  the  cabbage, 
and  the  lobulated  enlargements  of  the  turnip. 

Many  members  of  the  mustard  family,  Cruciferae,  are  subject 
to  the  attacks  of  this  fungus.  A  complete  list  of  the  hosts  upon 
which  it  has  been  found  cannot  be  given  on  account  of  the  fact 
that  much  information  has  been  covered  up  by  too  general  state- 
ments. In  the  United  States,  however,  it  certainly  occurs  upon 


FIG.  19.    CLUB  ROOT  OF  CABBAGE,  PRO- 
DUCED BY  PLASMODIOPHORABRASSIC&  WOR. 


MYXOMVCETES.    SLIME  MOLDS  99 

varieties  of  cabbage,  cauliflower  and  Brussels  sprouts  (Brassica 
oleracca),  turnip  (Brassica  campestris),  rutabaga  (Brassica  Rapa), 
radishes  (RapJianns  sativa),  and  certain  mustards  (Sinapis  and 
Brassica).  It  has  also  been  found  upon  such  weeds  as  shepherd's 
purse  (Caps  el  la  Bursa-pastoris}  and  hedge  mustard  (Sisymbrium 
officinalc).  In  Europe  besides  most  of  the  plants  mentioned  Mat  hi- 


FIG.  20.   A  CROSS  SECTION  OF  CABBAGE  ROOT  AFFECTED  BY  THE  CLUB 
ROOT  FUNGUS.  (Invaded  cells  enlarged  and  phloem  tissue  multiplied) 

ola  incana  and  Iberis  umbellata  are  hosts.  There  seems  to  be  little 
recent  data  of  interest  bearing  upon  the  comparative  susceptibility 
of  different  varieties  of  cultivated  plants.  Many  mistakes  have 
doubtless  been  made  in  assigning  to  this  fungus  injuries  appear- 
ing upon  other  orders  of  host  plants,  and  sometimes  even  those 
upon  crucifers,  due  to  nematode  worms.  It  is  often  difficult  to 
distinguish  between  the  two  causes  of  disease. 


96  FUNGOUS   DISEASES  OF  PLANTS 

groups  of  fungi  or  algae  ;  although  in  the  lowest  Phycomycetes, 
perhaps,  one  may  find  a  certain  questionable  similarity.  However, 
it  would  seem  that  the  closest  allies  of  the  Myxomycetes,  as  possi- 
bly of  some  of  the  lowest  Phycomycetes,  may  be  with  the  Flagel- 
lates. Finally  the  Myxomycetes  resemble  also  in  some  characters 
other  animal-like  groups,  such  as  the  Sporozoa  and  the  Myxospo- 
ridia.  It  is,  however,  unnecessary  here  to  enter  into  a  special  dis- 
cussion of  the  relationship  or  homologies  of  any  of  these  organisms. 


CHAPTER  VIII 

MYXOMYCETES.    SLIME   MOLDS 

I.  PHYTOMYXALES  (PHYTOMYXACE^E) 

In  the  family  Phytomyxaceae  are"  grouped  the  few  disease- 
producing  organisms  among  the  Myxomycetes.  The  family  is 
characterized  by  the  production  of  naked  masses  of  protoplasm 
(plasmodia)  within  the  cells  of  the  host.  The  plasmodium  gives  rise 
simultaneously,  or  by  a  successive  differentiation,  to  sphaeroidal 
spores,  and  the  germination  of  the  spore  produces  a  motile  swarm 
cell,  by  means  of  which  distribution  of  the  organism  is  effected. 
Generic  differences  are  found  almost  wholly  in  the  relation  of  the 
spores  one  to  another,  whether  single  or  grouped.  Plasmodiophora 
Brassiccz  is  the  only  well-known  species  of  economic  importance. 


II.    CLUB  ROOT  OF  CABBAGE  AND  OTHER  CRUCIFERS 
Plasmodiophora  Brassiccz  Wor. 

EYCLESHYMER,  A.  C.    Club-root  in  the  United  States.    Journ.  Myc.  7  :  79-87. 

pis.  15-16.    1892. 
HALSTED,  B.  D.    Club-root  of  Cabbage  and  its  Allies.    N.  J.  Agl.  Exp.  Sta. 

Built.  98:    1-16.  Jigs.  1-13.    1893. 
NAWASCHIN,  S.    Beobachtungen  tiber  den  feineren  Bau.  u.  Umwandlungen 

von  Plasmodiophora.    Flora  86 :  404-427.  pi.  20.    1899. 
WORONIN,  M.    Plasmodiophora  Brassicae.    Jahrb.  f.  wiss.  Bot.  11 :   548-574. 

pis.  19-24.    1878. 

The  club  root,  or  club  foot,  is  an  unsightly  and  destructive  root 
disease  of  crucifers  which  has  been  known  in  Europe  for  con- 
siderably more  than  a  century.  In  England  it  is  commonly  called 
fingers  and  toes,  anbury,  etc.  (Germany,  Kohlhernie ;  France, 
maladie  digitoire).  Our  knowledge  of  the  causal  relations  of  a 
Myxomycete,  Plasmodiophora,  to  the  disease  is  primarily  based 
upon  the  excellent  researches  of  Woronin  published  in  1878. 

Habitat  relations.  In  Europe  the  fungus  is  quite  generally 
distributed  throughout  the  market-gardening  sections.  In  1876 

97 


100 


FUNGOUS  DISEASES  OF  PLANTS 


zms 


Morphology.  Fungus  and  deformity.  The  parasite  is  sup- 
posed to  gain  entrance  to  the  host  plant  during  the  swarmspore 
stage,  or  immediately  upon  leaving  the  swarmspore  stage,  there- 
fore in  the  amoeboidal  form.  No  observations,  however,  have  been 

made  relative  to 
host  penetration, 
and  the  subject 
would  doubtless 
prove  an  interest- 
ing one. 

A  microscopic 
study  of  sections 
of    the    diseased 
root    shows   that 
the   organism    is 
most  abundant  in 
parenchymatous 
cells,  often  in  the 
vicinity    of     the 
cambium.    There 
FIG.  21.    STAGES    IN    THE    DIFFERENTIATION    OF   THE    is    in    quantity   an 
PLASMODIUM  AND  SPORES  IN  PLAS.IWD/OPHORA  BRASSIC^E    abnormal  develop- 
(After  Nawaschin) 

ment  of  phloem. 

The  xylem  portions  of  affected  roots  are  relatively  inconspicuous. 
According  to  some  observers,  certain  bundle  elements  may  also 
show  the  parasite. 

The  infested  cells  are  ordinarily  in  groups  (Fig.  20)  and 
Nawaschin  believes  that  these  groups  originate  by  the  division 
of  a  single  cell  and  that  such  groups  may  also  transmit  an  in- 
fluence to  similar  tissues  even  at  a  distance,  so  that  there  may 
eventually  result,  for  instance,  histological  disturbances  in  neigh- 
boring bundles.  It  is  possible,  however,  that  the  young  cells  of 
the  bundles  may  become  infected  and  that  the  organism  may  be 
enabled  to  maintain  itself  in  such  cells  for  a  time  after  differentia- 
tion of  the  latter  as  distinctive  bundle  elements. 

In  an  earlier  stage  the  contents  of  the  infected  cells  is  of  a  half- 
fluid  consistency,  later  turbid,  and  finally  granular.  Even  in  the 
first  stage  the  parasite  is  noticeable  in  the  amoeboidal  form  and 


MYXOMYCETES.   SLIME  MOLDS  101 

the  nuclei  may  be  distinct  (Fig.  21,  a).  The  number  of  amcebae  is 
increased  by  division,  probably  by  a  kind  of  budding  process.  Starch 
is  present  in  the  host  cells  but  the  amceba  gives  only  a  reaction  for 
oil.  No  migration  of  the  amoeboidal  stage  from  cell  to  cell  has 
been  observed.  Several  nuclei  are  present  in  each  amceba,  and  as 
the  number  of  the  latter  is  increased  they  become  rounded  and 
pressed  closely  together  into  what  is  practically  a  plasmodium. 
The  spore-forming  stage  is  then  initiated,  accompanied  first  by 
peculiarities  in  the  nuclei,  which  seem  to  disappear  more  or  less, 
according  to  Nawaschin  ;  and  this  stage  is  followed,  upon  again 
clearly  distinguishing  the  nuclei,  by  a  new  form  of  nuclear  divi- 
sion, mitotic  and  simultaneous  in  all  nuclei  (Fig.  21,  b  and  c). 
There  may  be  successive  simultaneous  divisions,  and  then  the  spores 
are  differentiated  by  the  formation  of  a  cell  wall  around  each  nucleus 
and  surrounding  cytoplasm.  Two  stages  in  the  differentiation  of 
the  spores  are  shown  in  Fig.  21,  d  and  e. 

Olive1  and  Jahn2  have  recently  described  what  seems  to  be  a 
sexual  process  in  certain  Myxomycetes  (notably  in  Ceratiomyxa). 
It  remains  to  be  seen  how  these  observations  will  finally  be  inter- 
preted, and  further,  if  there  may  also  be  fusion  of  the  nuclei  in 
the  case  of  Plasmodiophora.  In  this  connection  it  may  be  stated, 
however,  that  some  mycologists  doubt  the  relationship  of  Plasmo- 
diophora with  the  Myxomycetes. 

At  maturity  most  of  the  pathological  cells  are  packed  full  of 
the  spherical  thick-walled  spores,  and  the  latter  are  perhaps  set 
free  only  by  the  disintegration  of  the  roots.  Certain  unusual 
appearances,  moreover,  have  been  described,  but  these  are  not 
understood.  In  from  four  to  twenty-four  hours  the  spores  will 
germinate  in  water  in  which  some  of  the  host  tissue  has  been 
teased  out,  the  contents  of  each  spore  escaping  in  the  form  of  an 
irregular  protoplasmic  mass  which  may  quickly  change  its  form. 
There  is  at  first,  for  the  most  part,  an  appearance  of  an  elongated 
process  or  cilium,  which  doubtless  permits  rapid  motility,  denoting 
also  a  swarmspore  stage.  In  the  swarmspore  stage  a  nucleus  and 

1  Olive,  E.  W.    Cytological  Studies  on  Ceratiomyxa.    Trans.  Wis.  Acad.  Sci., 
Arts  and  Letters  15  (2)  :  753-774.    1907. 

2  Jahn,  E.    Myxomycetenstudien,  VI  Kernverschmelzungen.  .  .  .   Ber.  d.  Deut. 
Bot.  Ges.  25  :  23-26.    1907. 


102  FUNGOUS  DISEASES  OF  PLANTS 

a  pulsating  vacuole  are  always  seen.  Fig.  22  shows  a  spore  and 
some  swarmspore  stages.  Later,  the  protoplasmic  mass  moves 
wholly  by  amoeboidal  streaming.  It  is  believed  that  the  swarm- 
spores  may  fuse  into  small  amoeboidal  plasmodia  and  that  these  may 
also  gain  entrance  to  the  host.  Nevertheless,  the  true  plasmodial 

stage  is  apparently  that 
which  is  developed  im- 
mediately preceding 
spore  formation.  It  has 
been  noted  that  in  the 

FIG.  22.   PLASMODIOPHORA  BR ASSIGN:   SPORE,       same    cell   the   develop- 
GERMINATING  SPORE,  AND  SWARMSPORES 

ment  of   the  spores  is 

simultaneous,  and  this  may  be  true  also  of  a  whole  cell  group 
(Krankheitsherde)  occupying  an  area  so  large  as  to  be  visible  to 
the  unaided  eye.  So  it  would  seem  probable  that  we  may  look 
upon  a  plasmodium  as  extending  through  a  considerable  mass  of 
tissue.  The  mature  spore  possesses  a  refractive  wall,  or  membrane, 
the  contents  are  granular,  and  include  some  differentiated  bodies, 
or  globules,  the  nature  of  which  has  not  been  carefully  determined. 
Control.  On  account  of  the  fact  that  this  parasite  gains  en- 
trance through  the  soil,  numerous  experiments  have  been  made 
in  the  treatment  of  soils  with  lime,  sulfur,  and  other  fungicidal 
substances.  In  general  it  has  been  found  that  liming  is  the  most 
reliable  method  of  prevention,  lime  being  applied  to  ordinary  soils 
at  the  rate  of  about  one  hundred  bushels  per  acre  every  few  years. 
It  is  further  very  important  that  all  refuse  from  a  previous  crop 
should  be  destroyed.  It  is  especially  advisable  that  such  refuse 
should  not  be  thrown  upon  the  compost  heaps.  Rotation  of 
crops,  with  destruction  of  weeds  which  may  harbor  the  parasite, 
should  also  receive  attention. 


CHAPTER  IX 

SCHIZOMYCETES.    BACTERIA 

CHESTER,  F.  D.    A  Manual  of  Determinative  Bacteriology.    401  pp.  igo  figs. 
MIGULA,  W.    System   der  Bakterien  1:   368  pp.  6  pis.  1897;    2:    1069  pp. 

1 8  pis.    1900. 
SMITH,  ERW.  F.    Bacteria  in  Relation  to  Plant  Diseases.    Carnegie  Inst.  of 

Washington,  Publication  27  (Vol.  I):   285  pp.  31  pis.    145  figs.    1905. 
VAN  HALL,  J.  J.    Bijdragen  tot  de  kennis  der  Bakterieele   Plantenziekten. 

197  pp.    1902.    Amsterdam. 

The  Schizomycetes,  or  fission  fungi,  better  known  as  the 
bacteria,  embrace  numberless  species  of  microorganisms  which 
are,  perhaps,  morphologically  the  simplest  of  the  fungi.  These 
organisms  consist  of  minute  single  cells,  and  while  the  cells 
may  often  be  arranged  in  chains  or  filaments,  loosely  associated 
in  colonies,  or  temporarily  bound  together  in  sheaths,  there  is 
no  case  in  which  an  individual  may  be  looked  upon  as  more 
than  a  single  cell.  The  cell  forms  of  these  organisms  may  be 
constantly  assigned  to  one  of  only  three  general  types,  namely, 
spherical  (Coccus  type),  rod-like  (Bacillus  type,  varying  from 
spheroidal  to  long  rod-shape),  and  spiral  (Spirillum  type  or  screw 
form).  The  diameter  of  the  cells  of  the  coccus  forms  may  vary 
from  .3  to  3  /JL  (micromillimeters),  and  of  other  forms  from 
.3-4  x  i -20  yn,  the  maximum  being  attained  by  the  screw  form. 
These  organisms  play  an  exceedingly  important  role  in  the  econ- 
omy of  nature.  The  great  majority  are  saprophytic,  yet  many 
species  induce  diseases  of  animals.  A  relatively  small  number 
of  species  included  in  a  single  family  (so  far  as  present  knowl- 
edge goes)  produce  diseases  in  plants.  These  diseases,  however, 
rank  among  the  most  important  both  on  account  of  the  destruc- 
tive action  of  these  organisms  and  the  great  difficulty  experienced 
in  attempting  to  develop  effective  means  of  control.  The  number 
of  phytopathological  forms  is  annually  augmented,  and  it  is  proba- 
ble that  they  will  be  reckoned  as  relatively  more  important  as 
further  investigations  are  made. 

103 


104  FUNGOUS   DISEASES  OF  PLANTS 

Owing  to  the  simple  forms  of  these  organisms,  a  thorough 
knowledge  of  the  morphology  of  a  species  would  not  alone 
suffice,  even  roughly,  to  differentiate  the  numberless  more  or 
less  similar  species.  Fortunately,  the  development  of  pure-culture 
methods  has  made  possible  a  variety  of  tests,  or  points  of  com- 
parison. Growth  characteristics  of  colonies,  the  reactions  and 
products  on  numerous  culture  media,  the  thermal,  photal,  patho- 
logical, and  other  relations  of  the  germ  —  in  short,  all  physiolog- 
ical properties  —  must  be  studied  and  tabulated  in  order  to  make 
accurate  and  trustworthy  comparisons. 

Recently  a  descriptive  chart  has  been  prepared  for  the  Society 
of  American  Bacteriologists  l  which  indicates  concisely,  yet  com- 
pletely, the  characters  which  should  be  carefully  studied  and  tabu- 
lated in  the  case  of  any  organism  before  it  may  be  said  that  the 
organism  may  be  fully  and  properly  described.  This  chart  should 
be  in  the  hands  of  every  student  and  would  serve  as  a  score  card. 
In  short,  the  description  covers  general  morphology,  cultural  fea- 
tures, certain  physical  and  biochemical  characteristics,  and  patho- 
genic relations.  Under  morphology,  size,  form,  and  adherence  of 
the  vegetative  cells  are  noted.  The  nature  of  the  movement,  the 
type  of  endospores,  flagella,  capsules,  zooglcea,  involution  forms, 
and  staining  reactions  should  be  followed.  The  cultural  features 
include  a  complete  discussion  of  agar,  streak  and  stab  cultures,  and 
also  cultures  on  potato,  blood  serum,  gelatin,  beef  broth,  milk  or 
litmus  milk,  starch  jelly,  silicate  jelly,  a  special  study  of  the  colo- 
nies on  agar  and  gelatin,  and  the  special  growth  reactions  upon 
synthesized  nutrient  solutions. 

The  physico-chemical  features  are  concerned  with  the  produc- 
tion of  gases,  acids,  alkalis,  alcohol,  ferments,  etc.  ;  the  reduction 
of  nitrates,  or  the  presence  of  nitrites  or  nitrates  in  the  culture  ; 
indol-production,  resistance  toward  acids,  •  alkalis  and  other  toxic 
agents ;  vitality ;  and  temperature  relations,  particularly  the  thermal 
death  point,  the  maximum,  minimum,  and  optimum  for  growth. 

In  the  case  of  the  pathogenic  organisms,  a  complete  study  of 
infection,  the  relation  of  the  organism  to  the  legions  produced,  and 
special  reaction  of  hosts  and  parasite  should  be  considered. 

1  This  chart  was  prepared  by  F.  D.  Chester,  F.  T.  Gorham,  and  Erwin  F.  Smith, 
and  was  indorsed  by  the  Society  at  its  annual  meeting,  December  31,  1907, 


SCHIZOMYCETES.    BACTERIA 


This  is  accompanied  by  a  numerical  system  for  recording  the 
salient  characters  of  an  organism,  as  follows  : 

ioo.  Endospores  produced 

200.  Endospores  not  produced 

10.  Aerobic  (strict) 

20.  Facultative  anaerobic 

30.  Anaerobic  (strict) 

1.  Gelatin  liquefied 

2.  Gelatin  not  liquefied 

o.i  Acid  and  gas  from  dextrose 

0.2  Acid  without  gas  from  dextrose 

0.3  No  acid  from  dextrose 

0.4  No  growth  with  dextrose 

.01  Acid  and  gas  from  lactose 

.02  Acid  without  gas  from  lactose 

.03  No  acid  from  lactose 

.04  No  growth  with  lactose 

.00 1  Acid  and  gas  from  saccharose 

.002  Acid  without  gas  from  saccharose 

.003  No  acid  from  saccharose 

.004  No  growth  with  saccharose 

.0001  Nitrates  reduced  with  evolution  of  gas 

.0002  Nitrates  not  reduced 

.0003  Nitrates  reduced  without  gas  formation 

.0000 1  Fluorescent 

.00002  Violet  chromogens 

.00003  Blue  chromogens 

.00004  Green  chromogens 

.00005  Yellow  chromogens 

.00006  Orange  chromogens 

.00007  Red  chromogens 

.00008  Brown  chromogens 

.00009  Pink  chromogens 

.00000  Non-chromogenic 

.00000 1  Diastasic  action  on  potato  starch  (strong) 

.000002  Diastasic  action  on  potato  starch  (feeble) 

.000003  Diastasic  action  on  potato  starch  (absent) 

.000000 1  Acid  and  gas  from  glycerin 

.0000002  Acid  without  gas  from  glycerin 

.0000003  No  acid  from  glycerin 

.0000004  No  growth  with  glycerin 

(Pseudomonas  campestris  (Pam.)  Erw.  Smith  becomes  Ps.  21 1.333151.) 
The  bacteria  are  ordinarily  grouped  in  six  families,  arranged  in 
two  orders,  but  the  phytopathological  forms  are  included  in  the 
one  family  Bacteriaceae. 


I06  FUNGOUS   DISEASES  OF  PLANTS 

I.  BACTERIACE^: 

These  organisms  consist  of  cylindrical  or  occasionally  somewhat 
ovoidal  rod-like  cells,  straight  or  very  slightly  curved,  never  spiral. 
Growth  is  by  elongation  of  the  rod,  and  division  takes  place  by  a 
septum  (leading  to  a  fission)  perpendicular  to  the  direction  of  elon- 
gation. Separation  of  the  daughter  cells  may  take  place  in  such  a 
way  that  the  cells  may  commonly  be  single,  or  united  two  or  more 
in  a  chain.  Endospores  are  frequent,  rare,  or  wanting,  depending 
upon  the  species.  Motile  organs  (flagella)  may  or  may  not  be 
present. 

The  majority  of  the  important  plant  disease-producing  species 
thus  far  found  are  included  in  two  genera,  both  of  which  possess 
motile  organs,1  viz.  Pseudomonas2  and  Bacillus. 

Pseudomonas  Migula.  These  organisms  are  motile  by  means 
of  flagella  on  one  pole  of  the  cell  only,  the  flagella  varying  in 
number  from  I  to  10,  usually  1-3  (monotrichiate  or  lophotrichiate). 
Endospore  formation  is  relatively  rare. 

This  is  a  rather  comprehensive  genus  on  account  of  the  variability 
in  the  number  of  flagella,  varying  on  the  one  hand  towards  Bacil- 
lus, and  on  the  other,  when  the  rods  are  slightly  curved,  toward 
Microspira  of  the  spiral  forms.  Among  species  of  special  interest 
in  this  connection  are  the  following :  Pseudomonas  campestris 
(Pammel)  Erw.  Smith,  Pseiidomonas  Stewarti  Erw.  Smith,  Pseudo- 
monas Phaseoli  Erw.  Smith,  Pseudomonas  tumefaciens  (Erw.  Smith 
and  Townsend).  Pseudomonas  Olece  (Arcan.)  Trev.,  Pseudomonas 
Hyacinthi  (Wakker)  Erw.  Smith,  Pseudomonas  vascularum  (Cobb) 
Erw.  Smith,  Pseudomonas  Juglandis  Pierce,  Pseudomonas  mal- 
vaceanim  Erw.  Smith,  Pseiidomonas  Syringes  van  Hall,  and  Pseudo- 
monas Pruni  Erw.  Smith  may  also  be  mentioned. 

Bacillus  Cohn  (emend.).  These  organisms  are  motile  by  means 
of  wavy-bent  flagella  scattered  irregularly  over  the  cell(polytrichiate). 

1  A  few  species  of  the  nonmotile  genus  Bacterium  (Migula  emend.)  have  been 
described  as  of  phytopathological  interest,  among  which  are  Bacterium  teutlium 
Metcalf.    (Centrbl.  f.  Bakt.  Parasit.  u.  Infektionskr.    13  (II.  Abt.)  :  28-30.  1904; 
also  Neb.  Agl.  Exp.  Sta.  Kept.  17  :  69-112.    1904.) 

2  Smith  has  advanced  (Bacteria  in  Relation  to  Plant  Diseases,  pp.  168-171) 
strong  arguments  for  the  substitution  of  Bacterium  in  place  of  Pseudomonas ;  and 
he  would  establish  a  new  generic  name,  Aplanobacter,  for  the  nonmotile  forms 
generally  referred  to  Bacterium. 


SCHIZOMYCETES.    BACTERIA  107 

The  flagella  in  many  species  are  relatively  evanescent,  or  produced 
at  a  definite  period,  so  that  the  time  of  motility  may  be  brief.  The 
cells  are  more  commonly  united  into  short  threads  than  in  the  case 
of  the  preceding  genus.  Endospores  are  frequent.  Among  the 
species  of  much  importance  may  be  mentioned  the  following : 
Bacillus  amylovorus  Burrill,  Bacillus  tracheiphilus  Erw.  Smith, 
Bacillus  carotovorus  Jones,  Bacillus  aroidece  Townsend,  Bacillus 
solanacearum  Erw.  Smith,  Bacillus  Hyacinthi-septicus  Heinz, 
Bacillus  Cubonianus  Macch. 

II.    BLACK  ROT  OF  CABBAGE 
Pseudomonas  campestris  (Pammel)  Erw.  Smith 

CARMAN,  H.    A  Bacterial  Disease  of  Cabbage.    Ky.  Agl.  Exp.  Sta.  Rept.  3 : 

43-46.    1890. 
HARDING,  H.  A.    Die  schwarze  Faulnis  des  Kohls  und  verwandter  Pflanzen, 

eine  in  Europa  weit  verbreitete  Pflanzenkrankheit.    Centrbl.  f.  Bakt.  Par- 
ask.,  u.  Infektkr.  6(11.  Abt.):  305-313.    1900. 
HARDING,  STEWART,  PRUCHA.   Vitality  of  the  Cabbage  Black  Rot  Germ  on 

Cabbage  Seed.    N.  Y.  Agl.  Exp.  Sta.  Built.  251 :    177-194.    1904. 
PAMMEL,  L.  H.    Bacteriosis  of  Rutabaga  (Bacillus  campestris  n.  sp.).    Iowa 

Agl.  Exp.  Sta.  Built.  27:   130-135.  pi.  i.    1895. 
RUSSELL,  H.  L.    A  Bacterial  Rot  of  Cabbage  and  Allied  Plants.    Wis.  Agl. 

Exp.  Sta.  Built.  65:    1-39.  figs.  1-12.    1898. 
SMITH,  ERW.  F.    Centrbl.  f.  Bakt.  Parask.,  u.  Infektkr.  3(11.  Abt):  284-291, 

408-415,  478-486.  pis.  1-6.    1897. 
SMITH,  ERW.  F.    The  Black  Rot  of  the  Cabbage.    U.  S.  Dept.  Agl.,  Farmers' 

Built.  68:   i -2 1.    1898. 
SMITH,  ERW.  F.    The  Effect  of  Black  Rot  on  Turnips.    U.  S.  Dept.  Agl., 

Bureau  of  Plant  Industry,  Built.  29:    1-19.  pis.  1-13.    1903. 
STEWART,  F.  C,  and  HARDING,  H.  A.    Combating  the  Black  Rot  of  Cabbage 

by  the  Removal  of  Affected  Leaves.    N.  Y.  Agl.  Exp.  Sta.  Built.  232 : 

43-65.  pis.  1-2.    1904. 

Habitat  relations.  In  recent  years  this  cabbage  disease  has  be- 
come well  known  as  the  most  destructive  and  least  controllable 
cabbage  disease.  It  has  been  very  generally  reported  from  the 
states  of  the  Mississippi  Valley  and  eastward,  extending  into 
Canada  as  well.  It  is  also  well  known  in  Europe.  Possibly  a  form 
of  the  same  disease  may  occur  in  Japan  upon  radishes. 

It  has  been  shown  that  infection  takes  place  by  way  of  the  water 
pores  of  the  host.  In  accordance  with  this  fact,  the  climatic  con- 
dition favoring  the  entrance  of  the  organism  is  sufficient  moisture 
in  connection  with  warm  days  and  cool  nights.  This  would  favor 


108  FUNGOUS  DISEASES  OF  PLANTS 

the  suffusion  of  the  plant  with  water,  and  even  the  extrusion  of 
droplets  from'  the  pores.  Cool  weather,  warm,  dry  nights,  and  a 
dry  soil  offer  a  check  to  the  disease.  Smith's  careful  study  of 
water  pore  infections  has  contributed  greatly  to  our  knowledge  of 
the  method  of  bacterial  attack. 

Symptoms.  The  first  symptoms  in  the  leaves  are  manifested 1 
"  at  the  margins,  and  consist  of  yellowing  of  all  the  affected  parts 
except  the  veins,  which  become  decidedly  brown  or  black  [see 
Fig.  24].  The  leaves  appear  to  have  '  burnt  edges.'  From  the  mar- 
gin of  the  leaf  the  progress  of  the  disease  is  inward  and  downward 
through  the  stem.  It  usually  enters  the  latter  through  the  leaves. 


A  B 

FIG.  23.    BLACK  ROT  OF  CABBAGE.  (Photograph  by  F.  C.  Stewart) 
A,  inoculated  and  diseased  plant ;  J3,  control,  healthy 

Subsequently  the  disease  passes  out  again  from  the  infected  stem 
into  healthy  leaves  and  up  into  the  center  of  the  head.  If  leaves 
diseased  at  the  edges  are  pulled  off  and  examined  where  they  join 
the  stem,  the  groups  of  fibrovascular  bundles,  or  leaf  traces,  in  the 
petiole,  are  seen  to  be  either  free  from  the  disease,  in  the  early 
stage,  or  decidedly  brown  or  even  deep  black  from  its  presence. 
Leaves  attacked  in  this  manner  fall  off  prematurely  one  after 
another,  leaving  in  bad  cases  a  more  or  less  elongated  stem  cov- 
ered with  leaf  scars  and  crowned  with  a  tuft  of  small  leaves.  If 
the  disease  has  entered  the  stem  only  on  one  side,  that  side  is 
dwarfed  and  the  head  becomes  one-sided."  When  young  plants 

1  Smith.    The  Black  Rot  of  the  Cabbage,  /.  c.,  p.  6. 


SCHIZOMYCETES.    BACTERIA 


are  affected  they  may  be  killed.  Any  affected  plants  are  prey  to 
saprophytic  organisms,  and  an  offensive  soft  rot  is  then  likely  to 
result.  Whether  in  the  leaves  or  in  the  stem,  the  course  of  the 


FIG.  24.   A  CABBAGE  LEAF  WITH  BLACK  ROT  DEVELOPING  FROM  WATER 
PORE  INFECTIONS.  (Photograph  by  F.  C.  Stewart  and  H.  A.  Harding) 

disease  may  usually  be  traced  by  a  darkening  of  the  fibrovascular 
bundles.  Fig.  23  shows  a  healthy  and  a  diseased  plant,  the  latter 
as  a  result  of  artificial  infection.  Root  infection  may  also  occur. 

This  disease  has  been  found  upon  apparently  all  of  the  common 
varieties  of  cabbage,  in  regions  where  the  organism  has  gained  a 
strong  foothold.  Turnips,  cauliflower,  kale,  rape,  and  other  species 


I  IO 


FUNGOUS   DISEASES   OF  PLANTS 


of  cultivated  and  wild  cruciferous  plants   (such   as   mustard  and 
charlock)  are  also  known  to  be  susceptible. 

The  organism,  morphology  and  reactions.  Upon  gaining  entrance 
through  the  water  pores  upon  the  margins  of  leaves  this  organism 
multiplies  enormously.  It  is  probable  that  a  cellulose  enzyme  is 
slowly  secreted,  for  in  time  masses  of  bacteria  cause  the  progress- 
ive disappearance  of  the  cell  wall  in  contact  with  them.  Through 
the  vessels  of  the  fibrovascular  bundles  they  make  most  rapid  ad- 
vances. Affected  bundles  are  indeed  usually  chambered  pure  cul- 
tures of  this  organism,  and  poured  plate  cultures,  with  proper 
precautions,  show  a  remarkable  purity.  Upon  cutting  such  affected 


FIG.  25.  A  AND  £,  VASCULAR  BUNDLES  FROM  TURNIP  ROOT,  SHOWING  FORMA- 
TION OF  BACTERIAL  CAVITY  ;  C,  THE  BACTERIA.    (After  Erw.  F.  Smith) 

bundles  the  organism  may  ooze  out  in  yellow  droplets.  In  time 
practically  any  tissue  of  the  host  may  be  softened  and  disorganized 
(Fig.  25,  A  and  B\ 

The  organism  is  a  short  rod,  with  a  rather  long  flagellum  (Fig. 
25  C).  It  is  but  slightly  longer  than  broad  in  the  tissues  of  the  host, 
yet  in  artificial  culture  it  may  be  several  times  as  long  as  broad, 
measuring  0.7-3.0  x  0.4-0. 5/<t.  It  is  actively  motile  when  young 
and  nonmotile  with  age.  It  is  commonly  single  or  in  pairs,  and 
no  spores  have  been  found.  It  responds  readily  to  stains. 

It  grows  well  in  slightly  alkaline  bouillon,  developing  turbidity 
and  a  yellow  precipitate.  Gelatin  is  gradually  liquefied,  complete  in 
fifteen  days  at  17°  to  19°  C.,  with  yellow  precipitate.  On  feebly 


SCHIZOMYCETES.    BACTERIA  m 

alkaline  agar  (22°  Fuller's  scale)  colonies  are  circular,  pale  to  wax 
yellow  in  color,  margin  entire.  On  potato  there  is  a  copious,  flood- 
ing growth,  with  no  browning  of  the  substratum,  and  no  odor.  No 
acid  is  produced.  All  liquid  cultures  become  gradually  alkaline. 

The  optimum  growth  is  believed  to  be  at  25°  to  30°  C.,  and 
growth  is  feeble  at  5°  and  7°  C.  and  at  37°  and  38°  C.  It  is  killed 
by  an  exposure  of  ten  minutes  at  51°  C.  It  differs  from  Pseudo- 
monas  Hyacinthi,  to  which  it  is  related. 

It  is  believed  that  this  organism  is  able  to  pass  the  winter  in 
the  soil  of  fields  in  which  it  has  been  abundant.  The  suggestion 
has  also  been  made  that  it  may  be  disseminated  through  compost 
when  cabbage  refuse  has  contributed  to  the  compost  heap.  Re- 
cently it  has  been  demonstrated  that  some  of  these  germs  are  able 
to  live  over  on  the  seed  for  at  least  a  year. 

Control  measures.  The  most  dangerous  sources  of  infection  are 
the  infested  fields  and  the  seed  beds.  Seed  beds  should  be  watched 
carefully,  and  no  suspicious  plants  used.  A  rotation  of  crops  is 
the  sole  means  of  eradicating  the  organism  from  a  field  once  in- 
fested. Insects,  snails,  etc.,  may  spread  the  disease  to  some  extent. 
When  leaves  only  have  become  infected,  picking  these  and  burn- 
ing them  may  be  of  service,  although  in  most  instances  this  method 
has  proved  a  failure.  Seed  treatment  (mercuric  bichlorid  I  to  1000, 
fifteen  minutes  ;  or  formalin  I  to  200,  twenty  minutes)  is  advised. 

III.    WILT  OF  SWEET  CORN 
Pseudomonas  Stewarti  Erw.  Smith 

STEWART,  F.  C.    A  Bacterial  Disease  of  Sweet  Corn.    N.  Y.  Agl.  Exp.  Sta. 

Built.  130:  401-412.  pis.  1-4.    1897. 
SMITH,  ERW.  F.   Notes  on  Stewart's  Sweet-Corn  Germ  (Pseudomonas  steivarti 

n.  sp.).    Proc.  Am.  Assoc.  Adv.  of  Sci.  47:  422-426.    1898. 
SMITH,  ERW.  F.    U.  S.  Dept.  Agl.,  Div.  Veg.  Phys.  and  Path.  Built.  28:   i- 

153.    1901. 

This  disease  was  first  discovered  in  the  market  gardens  of  Long 
Island,  where  much  damage  was  done  to  sweet  corn,  Zea  mays. 
It  has  since  been  found  in  Iowa  and  reported  from  parts  of  New 
York,  so  that  it  is  doubtless  widely  spread.  It  is  entirely  distinct 
from  the  disease  of  field  corn  described  by  Burrill.1 

1  Burrill,  T.  J.  A  Bacterial  Disease  of  Corn.  111.  Agl.  Exp.  Sta.  Built.  6 : 
165-176.  1889. 


I  12 


FUNGOUS  DISEASES  OF  PLANTS 


Symptoms.  The  external  and  internal  symptoms  of  this  disease 
are  readily  noted  and  distinctive.  The  affected  plants  die  by  wilt- 
ing and  drying,  the  water  supply  being  cut  off.  Usually  the  leaves 
wilt  one  after  another  and  the  plant  may  live  a  month,  but  in  some 

cases  where  the  plants  affected 
are  a  foot  or  less  in  height  si- 
multaneous wilting  of  the  leaves 
may  result,  and  the  plants  may 
die  within  four  or  five  days 
of  the  first  appearance  of  the 
disease.  There  is  no  discolora- 
tion, decay,  or  other  complicat- 
ing symptoms. 

The  internal  evidence  of  dis- 
ease is  equally  clear.  Upon  cut- 
ting the  stem  lengthwise,  the 
"  fibro vascular-bundles  appear," 
according  to  Stewart,  "  as  yel- 
low streaks  in  the  white  paren- 


FIG.  26.    CROSS  SECTION  OF  STALK  OF 
SWEET  CORN,  SHOWING  BUNDLES  OCCU- 
PIED BY  BACTERIAL  COLONIES.    (Photo- 
graph by  F.  C.  Stewart) 


chyma ; 


but  in  the  stems  of 
plants  that  have  been  dead  for 
some  time  some  of  the  bundles 
may  be  black  instead  of  yellow.  If  the  stem  is  cut  crosswise  and 
the  cut  surface  exposed  to  the  air  for  about  five  minutes,  a  yellow 
viscid  substance  exudes  in  drops  from  the  ends  of  the  vessels." 
Except  for  the  greater  accuracy  of  poured  plates,  pure  cultures, 
which  are  essential,  might  be  made  by  direct  inoculation  into  tubes. 
The  appearance  of  diseased  bundles  in  cross  and  longitudinal  sec- 
tions is  illustrated  in  Figs.  26  and  27. 

Pathology.  The  organism  is  confined  to  the  fibrovascular  bun- 
dles exclusively,  and  appears  to  infest  only  the  vessels.  There  is 
no  disorganization  of  the  tissue,  and  the  pathological  effect  is  there- 
fore due,  in  large  part,  doubtless,  to  cutting  off  the  transpiration 
stream.  If  there  are  secondary  effects  felt  in  the  protoplasm  of 
rather  distant  living  cells,  and  brought  about  by  diffusion  of  inju- 
rious excreted  substances,  it  has  not  been  demonstrated,  so  far  as 
I  am  aware,  in  the  case  of  any  bacterial  disease  of  plants.  Field 
corn  and  pop-corn  are  resistant,  but  inoculation  experiments  with 


SCHIZOMYCETES.    BACTERIA  113 

sweet  corn  have  been  successful.  The  organism  is  probably  spread 
by  many  mechanical  agencies,  and  also  distributed  clinging  to  the 
seed. 

The  organism,  morphology  and  reactions.  The  rods  are  short, 
almost  ovoidal  in  form,  ordinarily  1.3-1.6  X  ./-.8  /JL.  On  agar 
the  colonies  are  more  or  less  circular,  becoming  lobulated  at  the 
margins.  With  age  the  surface  is  granular.  The  color  changes 
from  yellowish  white  to  bright  yellow.  Gelatin  is  not  liquefied.  A 


FIG.  27.    LONGITUDINAL  SECTION  OF  STALK  OF  SWEET  CORN, 
SHOWING  A  DISEASED  BUNDLE.    (Photograph  by  F.  C.  Stewart) 

vigorous  growth  is  produced  on  steamed  potato,  which  in  a  week 
is  iridescent.  The  potato  turns  brown  in  time. 

In  bouillon  a  turbidity  is  produced,  and  gradually  a  yellowish- 
white  precipitate  is  formed.  Yellow,  surface-colony  globules  appear. 
In  Uschinsky's  solution  there  is  a  vigorous  growth,  litmus  milk  is 
slowly  decolorized,  and  there  is  no  coagulation.  Gas  is  not  pro- 
duced, and  the  organism  is  aerobic  and  facultative  anaerobic. 

Control  measures.  There  is  great  difference  in  the  susceptibility 
of  varieties  of  sweet  corn,  and  this  may  be  made  use  of  where 
necessary.  Only  sound  seed  from  uninfested  regions  should  be 
employed.  A  rotation  of  crops  is  also  an  important  precautionary 
measure. 


114  FUNGOUS  DISEASES  OF  PLANTS 

IV.    CROWN  GALL  OF  APPLE,  PEACH,  AND  OTHER  PLANTS 
Pseudomonas  tumefaciens  Erw.  Smith  and  Tovvnsend  1 

HEDGCOCK,  GEO.  G.    Crown  Gall,  Hairy  Root  Disease  of  the  Apple.    Bureau 

Plant  Industry,  U.S.  Dept.  Agl.  Built.  90  (Pt.   II):    15-17.    pis.  j-j. 

1906. 
HEDGCOCK,  GEO.  G.    The  Cross  Inoculation  of  Fruit  Trees  and  Shrubs  with 

Crown  Gall.    Bureau  Plant  Industry,  U.  S.  Dept.  Agl.  Built.  131  (Pt.  Ill) : 

21-22.    1908. 
SCHRENK,  H.  VON,  and  HEDGCOCK,  GEO.  G.  The  Wrapping  of  Apple  Grafts 

and  its  Relation  to  Crown  Gall  Disease.    Bureau  Plant  Industry,  U.  S. 

Dept.  Agl.  Built.  100  (Pt.  II):   5-12.    1906. 
SELBY,  A.  D.    Diseases  of  the  Peach.    Ohio  Agl.  Expt.  Sta.  Built.  92 :  208- 

217.  pis.  5-6.    1898. 
SMITH,  ERW.  F.,  and  TOWNSEND,  C.  O.   A  Plant  Tumor  of  Bacterial  Origin. 

Science,  N.  S.  25:  671-673.    1907. 
TOUMEY,  J.  W.    An  Inquiry  into  the  Cause  and  Nature  of  Crown  Gall.    Ariz. 

Agl.  Exp.  Sta.  Built.  33:    1-64.  Jigs.  1-31.    1900. 
TOWNSEND,  .C.  O.    A  Bacterial  Gall  of  the  Daisy  and  its  Relation  to  Gall 

Formations  on  Other  Plants.    Science,  N.  S.  (Abstract)  29:   273.    1909. 

'Occurrence.  The  crown  gall -has  thus  far  been  found  most 
commonly  upon  rosaceous  plants  (Rosaceae),  among  these  being 
included  practically  all  of  the  stone,  pomaceous,  and  bush  fruits 
of  this  family,  especially  the  various  species  of  Prunus,  Pyrus, 
Rubus,  and  Rosa.  It  has,  however,  been  reported  upon  a  variety 
of  other  plants,  such  as  the  grap£  (Vitis  spp.),  walnut  (Juglans 
nigra),  chestnut  (Castanea  dentala],  poplar  (Populus  alba),  willow 
(Salix\  etc.  Thus  far,  very  little  striking  varietal  resistance  has 
been  reported,  although  it  is  probable  that  the  almost  total  absence 
of  the  disease  under  certain  conditions  is  to  be  attributed  in  part 
to  the  difference  in  the  susceptibility  of  the  hosts  as  well  as  to 
diversity  of  external  conditions.  In  general,  nursery  stock  is 
more  readily  affected  than  older  trees ;  but  this  may  be  due  to 
greater  opportunity  for  infection. 

1  It  seems  justifiable  to  give  as  conclusive  the  evidence  thus  far  presented  re- 
garding the  bacterial  nature  of  the  widespread  crown  gall.  This  evidence  has  been 
published  by  Smith  and  Townsend  only  as  a  preliminary  paper  and  as  abstracts  of 
reports  (one  cited  in  the  literature  above)  read  before  two  societies  at  the  meeting  of 
the  American  Association  for  the  Advancement  of  Science,  and  Affiliated  Societies, 
Baltimore,  December,  1908.  The  data  and  proofs  orally  presented,  however,  leave 
no  reasonable  doubt  as  to  the  bacterial  cause  of  a  large  number  of  gall  formations. 
It  is  not  yet  clear  whether  the  galls  of  all  such  plants  as  apple,  peach,  grape,  etc., 
are  due  to  the  particular  species  here  described,  or  to  closely  related  species.  This, 
however,  is  a  matter  of  far  less  present  significance. 


SCHIZOMYCETES.    BACTERIA  115 

Upon  different  hosts  the  galls  differ  only  slightly  in  form  and 
appearance.  Moreover,  they  are  generally  located  near  the  sur- 
face of  the  soil  in  the  region  of  the  collar.  A  gall  may,  however, 
develop  above  the  surface,  or  at  some  distance  below,  upon  the 
smaller  roots.  Superficial  galls  are  more  common  where  the  ex- 
posed portions  are  subject  to  such  injuries  as  those  produced  by 
rodents  or  the  implements  used  in  cultivation. 

Development  of  the  gall.  Published  results  regarding  the  de- 
velopment of  these  galls  are  based  upon  an  examination  of  woody 
plants.  It  is  probable  that  important  differences  will  be  found  in 
the  case  of  herbaceous  plants.  In  general,  the  gall  is  an  annual 
structure,  even  on  woody  plants,  beginning  its  growth  with  ex- 
foliation in  the  spring  and  maturing  more  or  less  by  the  time  of 
leaf  fall.  When  first  observed  the  hypertrophies  are  small  masses 
of  rapidly  growing,  almost  translucent  tissue,  nearly  spherical  in 
shape.  According  to  Toumey,  such  galls,  when  developed  super- 
ficially in  cultures,  may  become  greenish  from  the  presence  of 
chlorophyll.  In  any  event,  the  clear  white  appearance  is  lost  in 
a  few  months  and  the  gall  becomes  warty  and  browned.  During 
the  latter  part  of  the  season,  or  during  the  winter,  disintegration 
results,  apparently  by  a  normal  process  of  decay.  As  a  rule,  such 
galls  do  not  develop  secondary  galls  from  any  portion  of  the  old 
part  but  are  entirely  destroyed.  Young  galls  may,  however,  spring 
from  the  collar  or  roots  near  the  margin  of  the  gall  previously 
formed,  and  thus  the  wounds  and  injurious  effects  are  intensified 
from  year  to  year.  In  time  the  functions  of  the  conducting 
tissues  are  so  interfered  with  that  death  of  the  parts  above  follows 
gradually.  In  the  South  and  Southwest,  galls  which  begin  to  grow 
rather  late  in  the  season  may  continue  their  growth  throughout 
another  year. 

According  to  Toumey  "  when  the  gall  first  begins  its  develop- 
ment, there  is  a  pushing  outward  of  a  small  area  of  the  true 
cambium,  which  is  transformed  into  large  hypertrophied  paren- 
chyma cells.  ...  In  its  youngest  stages  the  tissue  of  the  gall 
is  a  mass  of  parenchyma  with  numerous  minute  areas  of  rapidly 
dividing  meristem  scattered  through  it.  The  areas  of  meristematic 
tissue  are  centers  of  growth.  ...  As  the  galls  become  older 
these  centers  of  growth  increase  in  size  and  others  originate  in 


Il6  FUNGOUS  DISEASES  OF  PLANTS 

the  newly  formed  parenchyma.  The  centers  of  these  growths  ulti- 
mately become  most  curiously  twisted  nodules  of  tracheides  and 
woody  fibers." 

Galls  upon  relatively  small  roots  may  not  attain  more  than 
a  centimeter  in  diameter,  while  ordinarily  on  nursery  stock, 

raspberries,  etc.,  they  may  be  as 
large  as  a  walnut  (Fig.  28).  On 
the  crowns  of  large  trees  they 
may  be  much  larger. 

Cross-inoculation  experiments. 
It  has  cost  no  small  amount  of 
-  effort  to  determine  the  cause 
of  crown  gall.  Tourney  found 
a  Myxomycete  developing  occa- 
sionally  upon  the  cut  surfaces  of 

FIG.  28.   CROWN  GALL  OF  PEACH       Sa"S    in    imPUre    CultUreS'      He 

further  observed  appearances  of 

the  protoplasm  in  certain  cells  of  the  parenchyma  of  young  galls 
suggesting  stages  in  the  development  of  the  plasmodia.  The  evi- 
dence was  not  strong,  however,  and  many  pathologists  reserved 
a  final  opinion  regarding  the  nature  of  this  disease.  It  was  long 
apparent  that  the  disease  is  infectious,  and  many  experiments 
demonstrated  that  it  could  be  conveyed  from  one  susceptible 
plant  to  another  by  inoculation  of  the  roots  with  macerated  galls 
or  by  burying  infected  parts  of  diseased  plants  in  the  vicinity  of 
healthy  roots.  The  results  of  rather  recent  and  extensive  inocula- 
tion experiments  by  Hedgcock  are  summarized  by  him  as  follows  : 

"  The  soft  galls  from  the  almond,  apricot,  blackberry,  cherry, 
peach,  plum,  prune,  and  raspberry  have  been  transferred  easily 
to  seedlings  of  the  almond,  apricot,  peach,  and  raspberry ;  less 
readily  to  those  of  the  blackberry,  cherry,  plum,  prune,  and  pear ; 
and  with  great  difficulty  to  seedlings  of  the  apple,  chestnut,  wal- 
nut, and  rose. 

"  The  soft  galls  of  the  apple,  chestnut,  walnut,  rose,  and  pear, 
as  a  rule,  have  not  been  transferred  readily  to  any  of  the  plants 
mentioned.  Evidence  has  been  obtained  of  a  wide  range  of  suscep- 
tibility in  different  varieties  of  the  same  plant.  This  has  been  noted 
in  varieties  of  the  apple,  blackberry,  cherry,  chestnut,  pear,  and  rose. 


SCHIZOMYCETES.    BACTERIA 


117 


"  The  results  of  these  experiments  show  that  the  opportunity 
presented  for  breeding  and  selecting  races  of  plants  resistant  to 
this  common  and  destructive  disease  is  excellent." 

Abundant,  substantial  proof  has  now  been  brought  forward  by 
Smith  and  Townsend  demonstrating  the  bacterial  nature  of  this 
disease.  This  work  resulted  from  an  examination  of  galls  appear- 
ing naturally  upon  the  Paris  daisy,  Chrysanthemum  frutescens. 
From  the  last-named  plant  they  were  able  to  isolate  a  species  of 
bacteria  which  proved  to  be  pathogenic.  They  reported  in  1907 
more  than  three  hundred  successful  inoculations  under  different 
conditions.  In  at  least  two  series  of  experiments  100  per  cent  of 
the  inoculations  were  effective,  control  plants  remaining  wholly 
free  from  galls  under  similar  conditions.  The  organism  was  then 
described  as  Bacterium  tumefaciens.  It  produces  hypertrophies 
very  readily  in  young  tissues,  particularly  in  fleshy  organs,  and 
it  sometimes  induces  abnormal  growths  on  the  wounded  parts 
of  young  cuttings.  This  organism  was  found  to  affect,  with  more 
or  less  similar  lesions,  many  plants,  including  the  tomato,  tobacco, 
potato,  sugar  beet,  grape,  carnation,  raspberry,  peach,  and  apple.  In 
four  or  five  days  after  inoculation,  swellings  were  evident,  the  latter 
on  the  daisy  attaining  an  inch  in  diameter  after  a  month  or  more. 

According  to  Townsend,  "  this  work  has  led  to  the  isolation  of 
pathogenic  Schizomycetes  from  the  galls  of  peach,  hard  galls  of 
apple,  hairy  root  of  apple,  hop,  rose,  and  chestnut.  The  organisms 
obtained  from  the  galls  of  these  different  plants  are  cross  inocula- 
ble  and  are  very  similar,  if  not  identical  in  size,  shape,  structure, 
and  habits  of  growth  on  media  with  the  organism  from  the  daisy 
gall."  It  is  further  ascertained  that  galls  produced  by  the  daisy 
organism  are  very  similar  to  those  formed  by  the  organism  from 
the  woody  plants.  It  is  apparent  that  it  is  too  early  to  expect 
definite  evidence  as  to  the  occurrence  of  biological  forms  or  other 
more  accentuated  differences. 

The  organism.  This  species  has  already  been  studied  with 
respect  to  its  reactions  on  various  media,  and  it  is  described  as 
a  short  rod,  motile  by  from  one  to  three  flagella.  Cultivated 
on  agar  the  translucent  white,  round  colonies  appear  slowly  at 
25°  C.  The  margins  are  smooth  and  dense.  It  produces  no  gas. 
Bouillon  is  not  heavily  clouded,  and  gelatin  is  not  liquefied.  The 


Il8  FUNGOUS  DISEASES  OF  PLANTS 

organism  grows  very  slowly  at  blood  heat,  but  shows  some  growth 
at  o°  C. 

Control.  It  has  been  found  very  difficult  effectively  to  cure 
trees  upon  which  the  gall  has  appeared.  Removal  of  the  gall 
with  the  tissues  adjacent  thereto,  and  the  use  of  antiseptic 
washes,  do  not  insure  the  complete  isolation  of  the  disease.  It 
is  evident,  therefore,  that  there  is  difficulty  in  removing  all  dis- 
eased tissues.  Since  the  gall  develops  promptly  in  nursery  stock, 
it  is  readily  detected  at  the  time  of  transplanting,  and  such  in- 
fected stock  will,  wherever  possible,  be  discarded.  Any  injuries 
to  growing  trees  at  or  near  the  surface  of  the  ground  will  make 
infection  easier,  and  consequently  care  should  be  taken  in  the 
cultivation  of  orchards. 

V.    OLIVE  KNOT,  OR  TUBERCLE-DISEASE  OF  THE  OLIVE 
Pseudomonas  Olece  (Arc.)  Trev. 

PETRI,  L.   Untersuchungen  iiber  die  Identitat  des  Rotzbacillus  des  Oelbaumes. 

Centrbl.  f.  Bakt.,  Parask.,  u.  Infektkr.  19  (Abt.  II):   531-538.    1907. 
PIERCE,  N.  B.   Tuberculosis  of  the  Olive.   Journ.  Myc.  6:   148-153.  pis.  14- 

15.    i 89 i . 
SAVASTANO,  L.    Tuberculosi,  iperplasie  e  tumori  dell'  olivo.    I  e  II  Memoria, 

Ann.  d.  R.  Scuola  Sup.  d'Agr.  in  Portici  5  :   131  pp.    1887. 
SMITH,  C.  O.   A  Bacterial  Disease  of  Oleander.   Bot.  Gaz.  42  :  301-310.    1906. 
SMITH,  ERW.  F.    Recent  Studies  of  the  Olive-Tubercle   Organism.    Bureau 

Plant  Industry,  U.  S.  Dept.  Agl.  Built.  131 :   25-43.    1908. 

The  olive  knot  was  known  in  early  times.  It  is  not  uncom- 
mon throughout  the  Mediterranean  region,  but  it  is  perhaps 
most  abundant  in  Italy.  It  seems  to  occur  also  in  California,. 
The  knot  is  conspicuous  from  the  development  upon  the  smaller 
twigs  and  branches  of  a  knob  or  tuberculate  swelling.  Small 
swellings  may  also  occur  on  the  leaves.  The  formation  of  the 
tubercle  usually  begins  in  the  spring,  and  where  the  tubercle 
surrounds  the  branch  the  latter  suffers  considerable  injury,  and 
may  eventually  die. 

Inoculation  experiments  made  with  pure  cultures  of  the  iso- 
lated organism  have  yielded  characteristic  infections,  both  in  the 
experiments  reported  by  Italian  investigators  and  in  those  of 
Erwin  Smith1  in  the  United  States.  C.  O.  Smith  has  studied 

1  Smith,  Erwin  F.    Bacteria  in  Relation  to  Plant  Diseases  1  :   10. 


SCHIZOMYCETES.    BACTERIA  119 

a  bacterial  disease  of  the  oleander  in  California,  and  from  cul- 
tural characters  of  the  organism  isolated,  as  well  as  from  inocula- 
tion experiments,  he  considers  this  organism  to  be  Pseudomonas 
Olece.  On  the  other  hand,  Erwin  Smith  would  regard  this  as 
improbable,  since  he  obtained  no  infections  on  oleander.  He 
would  seem  to  suggest  that  the  organism  isolated  in  California 
may  have  been  the  organism  of  crown  gall  (see  p.  114). 

VI.    BEAN  BLIGHT 
Pseudomonas  Phaseoli  Erw.  Smith 

BEACH,  S.  A.    Bean  Blight.    N.  Y.  Agl.  Exp.  Sta.  Kept.  11 :  553-555.'  1892. 

SMITH,  ERW.  F.  Description  of  Bacillus  Phaseoli,  n.  sp.  Proc.  Am.  Assn. 
Adv.  Sci.  46:  288-290.  1897. 

SMITH,  ERW.  F.  The  Cultural  Characters  of  Four  One-Flagellate  Yellow  Bac- 
teria Parasitic  on  Plants.  U.  S.  Dept.  Agl.,  Div.  Veg.  Phys.  and  Path. 
Built.  28  :  1-153.  1901. 

WHETZEL,  H.  H.  Some  Diseases  of  Beans.  Cornell  Agl.  Exp.  Sta.  Built. 
239:  197-214.  figs.  100-115.  1906. 

The  bean  blight,  a  disease  far  more  common  and  destructive 
in  the  United  States  than  has  been  generally  believed,  is  due  to 
this  organism.  The  disease  is  common 
upon  field,  garden,  and  lima  beans.  It 
affects  leaves,  stems,  and  pods,  but  par- 
ticularly the  leaves  and  pods,  upon  which 
the  symptoms  are  also  most  conspicuous. 
It  is  believed  that  diseased  seed  is  the 
source  of  many  early  infections,  whereas 
later  infections  may  result  through  wounds 
in  any  green  parts.  On  the  foliage  there 
appear  irregular  water-soaked  patches, 


which  later  become,  during  dry  weather,       FlG-  29-  PSEUDOMONAS 
brown   and    papery.     The   disease   pro-      J|££j£JkSSS! 
gresses  slowly,  therefore  it  becomes  evi- 
dent, as  a  rule,  only  when   the   pods  begin  to  form.    Control    is 
difficult,    and    must    concern    itself   largely   with    seed    selection 
and  crop   rotation.     Seed  from  an  affected  field  should  not  be 
planted.    It  is   not  enough   to   attempt  to  sort  out  healthy  seed, 
when    some  of   the   lot  are   evidently  diseased,  for  many  which 
show  no  discoloration  will  be  penetrated  by  the  bacteria. 


120  FUNGOUS  DISEASES  OF  PLANTS 

VII.    HYACINTH   DISEASE 
Pseudomonas  Hyadnthi  (Wakker)  Erw.  Smith 

SMITH,  ERW.  F.   Wakker's  Hyacinth  Germ  Pseudomonas  hyacinthi  (Wakker). 

U.  S.  Dept.  Agl.,  Div.  of  Veg.  Phys.  and  Path.  Built.  26:    1-45.   pi.  i. 

Ibid.  Built.  28  :    1-153.    I9°i- 
WAKKER,  J.  H.    Vorlaufige  Mitth.  tiber  Hyacinthenkrankheiten.   Bot.  Centrbl. 

14:  3 1 5-3 1 7.    1883. 
WAKKER,  J.  H.    Onderzoek  der  Ziekten  van  Hyacinthen,  en  andere  bol-en 

Knolgewassen  (1884):  4-13. 

This  organism,  apparently  confined  to  the  Netherlands,  is 
related  to  the  three  already  discussed,  yet  it  is  entirely  distinct. 
It  produces  a  disease  of  hyacinths,  entering  the  host  through 
wounds  or  through  the  nectaries.  The  vascular  system  is  chiefly 
affected,  but  the  neighboring  parenchymatous  tissue  is  gradually 
involved,  the  middle  lamellae  being  the  first  portions  of  the  walls 
to  succumb.  The  organism  may  require  a  year  in  which  to  destroy 
the  host. 

VIII.    BUNDLE  BLIGHT  OF  SUGAR  CANE 
Pseudomonas  vascularum  (Cobb)  Erw.  Smith 

COBB,  N.  A.    Diseases  of  the  Sugar  Cane.    New  So.  Wales  Dept.  Agl.  (1893): 

I— 21. 
SMITH,  ERW.  F.    Ursache  der  Cobb'schen  Krankheit.  des  Zuckerrohrs.    Cen- 

.trbl.  f.  Bakt.  Parasitenk.  u.  Infektionskr.  13  (II  Abt.) :  726-729.    1905. 

This  organism  is  the  cause  of  a  disease  of  the  sugar  cane. 
It  is  not  uncommon  in  Australia,  and  probably  also  in  Java, 
Brazil,  and  other  tropical  countries.  The  organism  attacks  the 
fibrovascular  bundles,  —  the  etiology  of  the  disease  is  not  unlike 
that  of  Pseudomonas  Stewarti  Erw.  Smith,  —  and  a  constant 
symptom  is  .the  excessive  development  in  the  bundles  of  a  yellow 
gum. 

IX.    PSEUDOMONAS:  OTHER  SPECIES 

Among  other  phytopathological  species  of  special  importance 
in  certain  regions,  yet  less  well  known,  or  imperfectly  reported 
upon,  are  the  following : 

Pseudomonas  Juglandis  Pierce  is  a  parasite  of  the  English  or 
Persian  walnut  (fiiglans  regia]  in  California.1'2  Young  nuts  and 
shoots  are  affected,  and  the  disease  is  one  of  much  importance. 

1  Pierce,  N.  B.    Walnut  Bacteriosis.    Bot.  Gaz.  31  :  272-273.    1901. 

2  Smith,  R.  E.   Report  of  the  Plant  Pathologist  to  July  i,  1906.    Calif.  Agl.  Exp. 
Sta.  Built.  184  :  232-236.  figs.  2-4.    1907. 


SCHIZOMYCETES.    BACTERIA 


121 


Pseudomonas  malvacearum  Erw.  Smith.  This  parasite  produces, 
through  stomatal  infections,  water-soaked,  angular  areas  (Fig.  30), 
known  as  angular  leaf  spot  of  cotton  (Gossypium).  Later  these 


FIG.  30.   ANGULAR  LEAF  SPOT  OF  COTTON.  (Photograph  by  Erwin  F.  Smith) 

spots  turn  purple  and  finally  become  dry  and  brown.  The  disease 
is  apparently  widely  distributed  in  the  southern  states,  but  the 
organism  has  not  yet  been  fully  described.1 

X.    PEAR  BLIGHT 
Bacillus  amylovorus  (Burrill)  De  Toni 

ARTHUR,  J.  C.    Diseases  of  the  Pear.    N.  Y.  Agl.  Exp.  Sta.  Rept.  3  :  357-367. 

1884. 
ARTHUR,  J.  C.    History  and  Biology  of  Pear  Blight.    Proc.  Phil.  Acad.  Nat. 

Sci.  (1886):  322-341.  pi.  j. 

BURRILL,  T.  J.    Trans.  111.  State  Hort.  Soc.  (1877):   114;  ibid.  (1878):  80. 
BURRILL,  T.  J.    Proc.  Am.  Assn.  Adv.  Sci.  29:  583.    1880. 

1  Smith,  Erw.  F.   Bacteria  in  Relation  to  Plant  Diseases  1  :  95,  126. 


122 


FUNGOUS  DISEASES  OF  PLANTS 


BURRILL,  T.  J.    Blight  of  Pear  and  Apple  Trees.    111.  Indus.  Univ.  Kept.  10  : 

583-597. 
JONES,  L.  R.    Studies  upon  Plum  Blight.    Centrbl.  f.  Bakt.  Paras,  u.  Infek- 

tionskr.  9  (Abt.  II):  835-841.    1902. 
WAITE,  M.  B.    Cause  and  Prevention  of  Pear  Blight.    Year  Book  U.  S.  Dept. 

Agl.  (1895):  295-300. 
WAITE,  M.  B.    Pear  Blight  and  its  Control  in  California.    State  Hort.  Com. 

of  Calif.  (Special  Report)  (1906):   1-20. 
WHETZEL,  H.  H.    The  Blight  Canker  of  Apple  Trees.    Cornell  Univ.  Agl. 

Exp.  Sta.  Built.  236:    103-138.  figs.  Jo-Sj.    1907. 

Pear  blight  has  been  known  in  the  United  States  for  more  than  a 
century.    Various  common  names  have  since  been  applied  to  this 

disease,  determined  largely 
by  the  host  plant  upon  which 
it  was  found,  and  by  the  par- 
ticular effect  produced  upon 
the  host.  Such  names  there- 
fore as  fire  blight,  twig  blight, 
blossom  blight,  and  other 
more  or  less  similar  designa- 
tions have  been  applied. 

Geographical.  This  disease 
was  first  reported  from  the 
northeastern  United  States, 
but  its  occurrence  was  subse- 
quently established  in  states 
to  the  south,  west,  and  south- 
west, and  by  1878  it  was  evi- 
dently very  well  established 
throughout  the  United  States 
east  of  the  Mississippi.  Still 
later  it  became  an  important 
bacterial  disease  in  the  far 


FIG.  31.   PEAR  TREE  PRACTICALLY  DEAD 

FROM  SEVERE  ATTACK  OF  PEAR  BLIGHT 

(Photograph  by  H.  H.  Whetzel) 

West  and  Southwest.  It  is  certainly  distributed  throughout  the 
United  States  at  present,  but  so  far  as  is  known,  it  does  not 
occur  in  Europe  or  in  Asia.  There  is  every  indication  that  the 
disease  had  its  original  home  in  the  eastern  United  States,  and  its 
original  host  was  doubtless  some  species  of  crab  apple  or  thorn  tree. 
Its  gradual  spread  westward,  therefore,  was  governed  by  the  spread 
of  civilization  and  the  consequent  greater  contiguity  of  orchards. 


SCHI2OMYCETES.    BACTERIA  123 

Host  plants.  This  species  has  received  the  name  of  pear  blight 
on  account  of  the  fact  that  it  is  a  more  disastrous  and  more  com- 
mon disease  upon  the  pear  (Pynis  communis)  than  upon  any  other 
of  its  numerous  hosts.  It  is  also  found  as  a  parasite  of  the 
apple  (Pyrus  Mains),  quince  (Cydonia  mdgaris),  and  of  numerous 
species  of  native  pomaceous  plants,  such  as  wild  crabs  (Pyrus) 
and  hawthorn  (Crataegus),  and  recently  it  has  been  found  on  the 
plum.  There  is  considerable  difference  in  the  susceptibility  of 
the  various  varieties  of  pears.  The  growing  of  Bartlett  and 
many  other  desirable  varieties  of  our  common  pears  in  the  south- 
ern states  and  in  the  Mississippi  Valley  has  been  very  largely 
given  up  on  account  of  the  destructiveness  of  this  disease.  Such 
varieties  as  the  Bartlett,  Seckel,  and  Le  Conte  are  much  more 
susceptible,  at  least  in  most  sections  of  the  country,  than  such 
as  the  Kieffer,  Duchess,  and  Winter  Nelis.  The  Oriental  group 
in  general  is  more  resistant,  although  the  several  varieties  are  by 
no  means  free  from  the  disease  under  conditions  favorable  for  its 
development  and  propagation. 

The  pear  blight  is  also  a  serious  disease  on  apples,  and  there 
seems  to  be  less  difference  in  resistance  among  these  fruits ; 
nearly  all  of  the  standard  varieties  being  more  or  less  affected. 

Symptoms.  The  pear  blight  is  more  commonly  noticed  during 
the  early  part  of  the  season,  when  it  appears  in  the  form  of  twig 
blight  throughout  the  blossoming  period  of  both  pears  and  apples. 
From  two  weeks  to  one  month  after  the  period  of  pollination  the 
blossoms  and  tips  may  begin  to  wilt  and  show  signs  of  general 
blackening,  resulting  finally  in  the  complete  blackening  and  death 
of  all  branches  or  spurs  upon  which  flower  clusters  have  been 
borne.  In  some  instances  scarcely  a  flower  tip  upon  an  infested 
tree  is  free  from  this  general  attack.  As  a  matter  of  fact,  the  in- 
fection usually  takes  place  at  the  time  of  blossoming  and  the  dis- 
ease fs  most  abundantly  distributed  at  that  time,  as  will  be  shown 
later.  Upon  the  pear  the  blight  may  continue  to  extend  down  the 
twig  or  the  branch,  the  branch  being  entirely  killed  as  it  progresses  ; 
and  in  the  course  of  some  months  it  may  have  extended  into  the 
larger  limbs,  or  into  the  main  body  of  the  tree  (Fig.  31).  Water 
shoots  may  also  be  affected  both  in  the  case  of  the  pear  and  the 
apple  (Fig.  32),  and  direct  entrance  to  the  body  gained  after  a 


1*4 


FUNGOUS  DISEASES  OF  PLANTS 


very  short  period  of  growth.  Nevertheless,  under  conditions 
more  favorable  for  the  host  plant  the  blight  may  never  extend 
more  than  a  few  inches,  resulting  merely  in  a  tip  pruning.  In 
the  case  of  the  apple  this  twig  blight  is  the  rule,  the  disease 
apparently  being  usually  unable  to  maintain  itself  in  the  larger 
branches.  Young  fruits  of  the  apple,  an  inch  in  diameter,  are 


FIG.  32.  WATER  SPROUTS  OF  APPLE  KILLED  BY  BLIGHT 

frequently  affected ;  and  the  copious  growth  of  the  organism 
gorges  the  fruit  with  the  slime  which  may  be  exuded  in  droplets. 
The  progress  of  the  disease  is  ordinarily  very  clearly  indicated 
by  the  appearance  of  the  bark.  The  growth  of  the  organism 
within  the  tissues  of  the  soft  bark  causes  a  water-soaked  appear- 
ance, and  finally  a  blackening  and  shriveling.  The  organism 
may,  however,  extend  to  a  distance  of  several  inches,  or  even 
a  foot,  below  the  water-soaked  area.  When  the  organism  ceases 
to  spread  rapidly  in  the  tissues,  a  sharp  line  of  demarcation  is 
noticeable,  separating  the  dead  from  the  healthy  or  comparatively 


SCHIZOMYCETES.    BACTERIA 


125 


healthy  tissues.  In  many  instances  the  bark  is  broken,  due  proba- 
bly to  a  gelatinizing  process  set  ,up  by  the  organism  in  the  tissues 
of.  the  host ;  and  from  these  ruptured  areas  there  are  exuded  beads 
of  a  gelatinous  or  gummy  nature,  varying  in  color  from  milky 
white  to  brown  or  black.  In  order  to  secure  cultures  when  the 
disease  is  not  very  active,  it  will  be  found  desirable  to  bring 
affected  twigs  into  the  laboratory,  placing  them  under  a  bell  glass 
with  the  basal  ends  in  a  vessel  of  water. 

The  organism.  The  general  life  history  of  Bacilhis  amylovorus 
upon  its  host  has  become  a  landmark  in  our  knowledge  of  bac- 
terial diseases.  The  relations  of  this  organism  to  the  disease  have 
been  under  constant  observation  for  about  thirty  years.  The  true 
cause  of  the  disease  was  first  suspected  in  1877  (Burrill),  and  the 
final  discovery  that  pear  blight  is  due  to  a  species  of  bacteria  was 
of  unusual  significance,  as  it  shared  with  the  discovery  made  by  a 
Dutch  botanist  (Wakker)  the  h6nor  of  constituting  the  pioneer 
work  with  bacteria  from  a  phytopathological  standpoint. 

The  most  careful  observations  and  experiments  indicate  that 
the  chief  source  of  infection  is  by  means  of  the  visits  of  insects, 
especially  bees,  to  the  blossoms.  The  infection  occurs,  therefore, 
at  the  time  of  pollination.  The  bacillus  multiplies  very  rapidly  in 
the  nectary  of  the  flower,  in  which  germs  are  directly  inoculated 
by  the  visits  of  the  insects.  The  rapid  growth  of  the  organism  is 
such  that  after  being  inoculated  into  a  blossom,  and  multiplying 
therein  for  twenty-four  hours,  it  might  be  spread  during  the  next 
day  to  many  thousands  of  blossoms.  From  the  nectary  it  gains 
entrance  into  the  softer  tissues  of  the  bark  and  cambium,  where 
it  is  very  largely  confined.  Nevertheless,  it  is  also  true  that  in- 
fection may  result  through  the  growing  twigs.  Biting  or  piercing 
insects  are  doubtless  of  much  importance  in  spreading  the  disease 
in  this  way.  Injuries  and  sometimes,  perhaps,  even  water  pores 
may  be  the  seats  of  infection.  In  general,  however,  it  is  certainly 
true  that  the  presence  of  germs  upon  the  surface  of  healthy  tissues 
would  not  result  in  the  production  of  disease  in  those  parts. 

The  bacillus  winters  over,  under  favorable  conditions,  in  rela- 
tively few  affected  branches,  under  conditions  where  moisture 
is  sufficient  and  protection  from  drying  out  adequate.  It  is  from 
such  wintered-over  areas  as  centers  that  the  disease  is  spread  to 


126  FUNGOUS  DISEASES  OF  PLANTS 

the  blossoms  the  following  spring.  With  the  return  of  growing 
conditions,  fermentation  may  be  set  up  and  beads  of  the  gummy 
exudation  produced.  Since  the  beads  contain  countless  quantities 
of  the  bacillus,  insects  readily  spread  it  to  some  blossoms ;  thence 
it  is  promptly  carried  by  bees  to  greater  distances.  The  organism, 


FIG.  33.   PEAR  FRUIT  INFESTED  WITH  THE  BLIGHT  ORGANISM  ;  BEADS 
EXUDED  IN  MOIST  CHAMBER.    (Photograph  by  H.  H.  Whetzel) 

however,  is  not  very  resistant  to  conditions.  It  is  killed  by  very 
brief  exposure  to  sunlight  and  by  a  period  of  drying.  This  latter, 
however,  seems  remarkable,  in  view  of  the  general  experience  that 
no  amount  of  cold  can  act  unfavorably  upon  this  organism.  It  is 
possible,  however,  that  the  effect  of  cold  in  the  absence  of  mois- 
ture may  be  as  disastrous  as  drying  out. 

The  characteristics  of  this  organism  according  to  Whetzel  are 
as  follows : 


SCHIZOMYCETES.    BACTERIA  127 

Single  cells  of  the  organism  direct  from  the  tree  are  oval,  1.5 
to  2  ^  long,  and  somewhat  more  than  half  as  broad  (Fig.  34). 
They  occur  single  or  attached,  several  end  to  end.  Upon  various 
culture  media  they  are  more  commonly  single  or  in  pairs,  al- 
though sometimes  in  short  threads,  and  in 
all  cases  motile  in  fresh  cultures. 

On  gelatin  growth  is  slow,  requiring  three 
to  five  days  for  the  appearance  of  colonies, 
the  latter  being  globose  to  lenticular,  yellow- 
ish, liquefying  the  medium  very  slowly.  : 

On  agar  the  surface  colonies  appear  more 

rapidly,  being  evident  the  second  day,  and  FIG.  34.  LLUS  AMY- 
attaining  a  diameter  of  from  2  to  3  mm.  by  LOVORUS  FROM  APPLE 
the  fourth  or  fifth  day.  They  are  white  and  FRUIT'  SIMPLE  STAIN 
granular,  or  cloudy,  with  a  sharply  defined  white  center ;  the  mar- 
gins are  entire  or  slightly  wavy,  with  a  dense  white  center.  Immersed 
colonies  are  globose  or  lens-shaped,  and  opaque-yellowish. 

In  bouillon  a  cloudiness  is  produced  after  twenty-four  hours, 
and  this  is  accompanied  by  slight  acidity  ;  after  forty-eight  hours 
there  is  greater  cloudiness,  with  more  or  less  persistent  flocci, 
the  medium  becoming  alkaline,  and  in  time  showing  a  tendency 
to  clear.  In  sugar-free  bouillon  the  liquid  remains  clear  for 
twenty-four  hours,  except  for  slight  sediment.  It  is  neutral  at 
first,  becoming  cloudy  and  alkaline  after  some  days.  In  milk 
no  change  is  evident  until  the  third  or  fourth  day,  when  thick- 
ening begins,  which  increases  to  fifth  or  sixth  day.  The  product 
finally  becomes  subgelatinous,  and  in  ten  days  there  is  a  clear 
liquid  above.  This  is  at  first  acid,  becoming  slightly  alkaline. 
Litmus  milk  is  unchanged. 

On  slanting  agar  tubes  growth  in  twenty-four  hours  is  moderate, 
opalescent,  spreading  slowly,  producing  turpidity  in  the  water  of 
condensation  ;  growth  not  viscid. 

On  gelatin  stab  cultures  growth  is  similarly  slow,  and  beaded 
or  granular  along  the  needle  path ;  surface  growth  with  irregular 
or  erose  margin,  center  thin  and  granulose ;  liquefaction  slow, 
crateriform  and  stratiform. 

Control.  The  control  of  pear  blight  was  for  a  long  time  con- 
sidered impossible,  but  careful  study  under  various  conditions 


128 


FUNGOUS  DISEASES  OF  PLANTS 


(particularly  the  work  of  Waite)  has  shown  that  this  disease 
may  be  controlled  or  even  practically  eradicated  in  large  regions. 
The  essential  step  consists  in  pruning  out  the  blight  in  situations 
where  it  may  winter  over.  If  all  of  the  blight  could  be  thoroughly 
pruned  out  of  the  orchard  during  the  fall  and  winter,  there  would 


FIG.  35.    BLIGHT  CANKER  ON  TRUNK  OF  APPLE,  FROM  INFECTED  PRUN- 
ING KNIFE.    (Photograph  by  H.  H.  Whetzel) 

probably  be  no  opportunity  for  infection  the  following  season,  ex- 
cept from  distant  orchards.  In  practice  the  pruning  out  of  the 
blight  during  winter  is  not  an  easy  process,  and  it  requires 
the  greatest  care  and  keenest  eyesight.  It  would  be  necessary 
to  go  over  the  orchard  several  times,  the  final  observation  being 
made  only  a  short  time  before  the  opening  of  the  blossoms. 


SCHIZOMYCETES.    BACTERIA  129 

Pruning  during  the  growing  season  is  also  practiced,  but  it  is  less 
reliable.  Such  pruning  has  not  proven  a  great  success  on  account 
of  the  fact  that  infection  may  be  constantly  taking  place.  More- 
over, when  the  blight  is  rapidly  extending  in  a  limb  or  trunk,  it 
is  difficult  to  determine  the  extent  of  the  region  affected.  In  deal- 
ing with  this  organism,  in  general,  all  possible  bacteriological  pre- 
cautions must  be  taken.  Carelessness  in  the  pruning  of  nursery 
stock  may  actually  result  in  spreading  the  disease  to  practically 
all  of  the  young  trees.  The  knife  should  be  promptly  applied 
wherever  a  limb  or  trunk  may  be  saved,  and  antiseptic  precau- 
tions should  be  taken. 

XI.    WILT  OF  CUCURBITS 
Bacillus  tracheiphilus  Erw.  Smith 

SMITH,  ERW.  F.  Bacillus  tracheiphilus,  sp.  nov.,  die  Ursache  des  Verwelkens 
verschiedener  Cucurbitaceen.  Centrbl.  f.  Bakt,  Parasitenk.  u.  Infektskr. 
l(Abt.  II):  364-373-  1895- 

The  wilt  of  cucurbits  was  first  reported  about  1893  (Smith)  and 
it  is  now  the  most  common  and  perhaps  the  most  serious  disease 
among  cucurbitaceous  plants  in  the  United  States.  It  was  at  first 
known  (to  pathologists  at  least)  in  the  northeastern  states,  but  it 
is  now  common  upon  several  hosts  in  Missouri,  Colorado,  and 
other  western  states.  Cucumbers  and  melons  would  seem  to  be 
most  susceptible,  although  pumpkins  and  squash  may  be  attacked. 
Weather  conditions  do  not  seem  to  affect  materially  the  abun- 
dance of  this  disease. 

Symptoms.  The  general  symptoms  are  simple  and  striking. 
These  consist  of  a  progressive  wilting  of  the  host.  If  infection 
takes  place  upon  the  central  stem,  the  wilting  in  the  whole  vine 
follows  promptly.  If,  however,  infection  is  in  the  distal  parts., of 
branches,  there  is  gradual  wilting  back  to  the  main  stem.  Then 
the  remaining  branches  promptly  show  the  effect.  In  the  tissues 
there  is  at  the  time  of  wilting  very  slight,  if  any,  evidence  of  a 
change  in  appearance.  In  no  case  is  there  the  development  of 
odors,  or  of  decay  in  the  usual  sense. 

Infection  and  spread  of  the  disease  appears  to  result  almost 
wholly  through  biting  insects.  The  organism  is  found  massed 
primarily  in  the  vessels  of  the  xylem.  At  first  the  spiral  vessels 


130  FUNGOUS  DISEASES  OF  PLANTS 

are  the  seat  of  action,  and  later  the  pitted  vessels  are  infested. 
In  late  stages  of  the  disease  the  lesions  may  be  considerable,  the 
bundle  system  being  broken  down  and  cavities  formed  in  the  ad- 
jacent tissues.  The  lesions  are  also  very  noticeable  when  the 
organism  has  gained  entrance  to  the  fruit. 

The  organism  is  a  rod  averaging  two  or  three  times  as  long 
as  broad,  1.2-2.5  X  .$-.?,  often  adhering  in  twos,  and  rapidly 
motile  only  when  young  (Fig.  37).  The  rods  are  readily  stained 


FIG.  36.    BACTERIAL  WILT  OF  MELONS.    (Photograph  by  H.  H.  Whetzel) 

with  carbol  fuchsin,  but  the  flagella  are  not  so  readily  demon- 
strated. Growth  in  bouillon  results  in  a  turbidity,  and  in  potato 
decoction  viscosity  is  developed  with  age.  Coagulation  of  milk 
does  not  occur,  and  after  weeks  no  viscosity  is  evident.  On 
gelatin  growth  is  slow,  and  there  is  no  liquefaction.  Similarly, 
on  agar  the  clear,  or  milk-white,  colonies  spread  slowly.  Stab 
cultures  develop  a  slight  growth  throughout  the  extent  of  the 
stab,  with  lobulated  projections.  On  slices  of  potato  there  is  a 


SCHIZOMYCETES.    BACTERIA  131 

vigorous  gray-white  film,  and  no  changes  are  manifest  in  the 
substratum.  The  organism  is  aerobic  and  perhaps  facultative 
anaerobic.  There  is  no  gas  production. 

The  contents  of  the  vessels  affected  are  slightly  alkaline,  and 
alkaline  media  are  apparently  preferred.  This  organism  is  sensi- 
tive to  high  temperatures,  43°  C.  or  over 
being  fatal  in  ten  minutes.  Death  results  in 
fifteen  minutes  in  dry  air,  and  the  normal 
life  of  a  culture  is  from  a  few  weeks  to  'FlG  37  BACILLUS 
several  months. 

Numerous  well-controlled  infection  experiments  have  established 
the  causal  connection  of  the  bacillus  with  the  symptoms  of  this 
disease. 

XII.    SOFT  ROT  OF  CARROT  AND   OTHER  VEGETABLES 
Badlhis  carotovorus  Jones 

HARDING,  H.  A.,  and  STEWART,  F.  C.  A  Bacterial  Soft  Rot  of  Certain  Cru- 
ciferous Plants  and  Amorphophallus  simlense.  Science,  N.  S.  16:  314- 
315.  1902. 

HARRISON,  F.  C.  A  Bacterial  Disease  of  the  Cauliflower  (Brassica  oleracea] 
and  Allied  Plants.  Ont.  Agl.  Exp.  Sta.  Built.  137 :  1-28.  figs.  1-18.  1904. 

JONES,  L.  R.  A  Soft  Rot  of  Carrot  and  Other  Vegetables.  Vermont  Agl.  Exp. 
Sta.  Rept.  13:  299-332.  Jigs.  i-io.  1901. 

POTTER,  M.  C.  Ueber  eine  Bakterienkrankheit  der  Ruben  (Brassica  Napus\ 
Centrbl.  f.  Bakt.,  Parasitenk.  u.  Infektionskr.  7  (Abt.  II):  282-288,  353- 
362.  1901. 

SPIECKERMANN,  A.  Beitrag  zur  Kenntnis  der  bakteriellen  Wundfaulnis  der 
Kulturpflanzen.  Landw.  Jahrb.  31 :  155-178.  1902. 

VAN  HALL,  C.  J.  J.  Bijdragen  tot  de  Kennis  der  Bakterieelle  Plantenziekten : 
176-184.  1902. 

Occurrence  and  effects.  This  bacillus  appears  to  be  one  of 
the  most  common  and  widespread  of  the  species  parasitic  upon 
plants.  It  was  not  accurately  studied  until  1901,  but  has  since 
received  attention  from  a  number  of  investigators  in  different  parts 
of  Europe  and  America.  It  seems  safe  to  say  that  it  is  the  chief 
producer  of  that  type  of  disease  known  as  soft  rot  in  vegetables.1 

1  Through  the  kindness  of  Mr.  H.  A.  Harding,  of  the  New  York  Agricul- 
tural Experiment  Station,  I  have  been  able  to  see  the  proof  of  a  bulletin  by 
H.  A.  Harding  and  W.  J.  Morse  on  the  morphology  and  cultural  characters  of 
this  organism.  This  study  establishes  in  a  conclusive  manner  the  fact  that  many 
diseases  of  vegetables  previously  referred  to  other  organisms  are  in  reality  properly 
caused  by  this  species,  and  the  data  here  presented  are  largely  based  upon  the 
study  indicated, 


132  FUNGOUS   DISEASES   OF  PLANTS 

The  bacteria  invade  the  intercellular  spaces  of  the  host,  and 
subsequently  the  tissues  are  rapidly  disorganized.  This  disorgani- 
zation is  apparently  due  to  an  enzyme  which  attacks  particularly 
the  middle  lamella.  A  large  number  of  inoculation  experiments 
have  been  made,  and  it  is  clearly  shown  that  these  bacteria  are 
able  to  produce  a  form  of  soft  decay  in  a  great  variety  of  plants. 
No  other  organism  yet  found  has  such  a  wide  range  of  host  plants. 
Morphology  and  cultural  characters.  The  bacillus  is  in  the 
form  of  short  or  long  rods  or  chains.  According  to  Jones  it 

measures  .6 -.09  x  1.5-5  A1,  the  niajor- 
ity,  however,  measuring  .8 x 2 p.  No en- 
dospores  are  produced,  and  it  possesses 
from  two  to  ten  peritrichiate  flagella. 

Upon  slanting  tubes  of  agar  an  abun- 
dant growth  is  produced.  This  is  fili- 
form to  spreading,  smooth  or  contoured,, 
and  opaque  to  opalescent  in  appear- 

ance-  !t  also  g™8  wdl  on  potato- 

Gelatin  is  promptly  liquefied,  under 
ordinary  circumstances,  at  20°  C.  Usually  liquefaction  begins  on 
the  second  day  and  is  complete  in  six  days  ;  yet  months  may  be 
required.  In  bouillon  a  pellicle  is  often  formed.  In  other  cases 
there  is  merely  a  clouding,  or  finally  the  development  of  a  floccu- 
lent  precipitate.  Milk  is  usually  coagulated  by  the  third  day,  and 
this  is  so  slowly  peptonized  that  the  action  may  not  be  complete 
for  several  months.  Litmus  milk  is  rendered  acid,  and  the  power 
of  indol  production  is  possessed  to  a  feeble  extent. 

The  organism  reduces  nitrates  in  nitrate  broth  to  nitrites.  The 
thermal  death  point  is  about  48  to  50°  C.  It  is  also  important  to 
note  that  with  a  majority  of  the  strains  gas  is  produced  in  small 
amounts  with  dextrose,  lactose,  and  saccharose.  In  this  gas- 
producing  character  the  forms  of  the  organism  from  a  large 
number  of  sources  show  a  certain  variation,  however,  which 
reaches  an  extreme  in  the  form  producing  soft  rot  of  the  calla 
lily,  in  which  case  no  gas  is  produced  from  any  of  the  sugars 
mentioned.  The  calla  lily  organism  is  tentatively  retained  as  a 
distinct  species.  It  represents,  at  any  rate,  an  extreme  form  of 
the  Bacilhis  carotovorus  so  far  as  it  is  at  present  known. 


SCHIZOMYCETES.    BACTERIA  133 

XIII.    SOFT  ROT  OF  THE  CALLA 
Bacillus  aroidecz  Townsend 

TOWNSEND,  C.  O.    A  Soft  Rot  of  the  Calla  Lily.    U.  S.  Dept.  Agl.,  Bureau 
Plant  Industry,  Built.  60 :    1-44.  pis.  i-g.    1904. 

This  organism,  very  closely  related  to  the  preceding,  has  been 
found  to  be  the  cause  of  a  serious  soft  rot  of  the  calla  lily, 
destroying  the  plants  at  about  the  time  of  flowering.  The  seat 


FIG.  39.    ISOLATION  CULTURE  OF  BACILLUS  AROIDEA?  TOWNSEND. 
(Photograph  by  C.  O.  Townsend) 

of  the  disease  is  principally  in  the  corms,  petioles,  and  flower 
stalks.  If  inoculated  into  a  wound,  the  bacillus  will  produce  a 
rot  in  many  raw  vegetables,  and  also  in  some  green  fruits.  The 
cultural  characters  have  been  indicated.  According  to  Town- 
send  it  produces  on  agar  very  characteristic  radiate  colonies 
(Figs.  38,  39)  at  or  near  the  optimum  temperature.  The  rot 
in  the  calla  may  be  prevented  by  a  careful  selection  of  the  corms 
and  by  changing  the  soil  in  the  beds  every  three  or  four  years. 


134 


FUNGOUS  DISEASES  OF  PLANTS 


XIV.    WILT  OF  SOLANACE^: 
Bacillus  solanacearum  Erw.  Smith 

SMITH,  ERW.  F.  A  Bacterial  Disease  of  the  Tomato,  Egg  Plant  and  Irish 
Potato.  U.  S.  Dept.  Agl.,  Div.  Veg.  Phys.  and  Path.  Built.  12:  1-26. 
pis.  1-2.  1896. 

SMITH,  ERW.  F.  The  Granville  Tobacco  Wilt.  U.  S.  Dept.  Agl.,  Bureau 
Plant  Industry,  Built.  141  (Pt.  II):  17-24.  1908. 

This  is  a  germ  which,  in  the  United  States,  causes  an  important 
wilt  and  drying  up  of  potatoes,  tomatoes,  and  eggplants.    In  the 

far  South  it  is  particularly  destruc- 
tive to  tomatoes.  It  has  also  been 
found  in  Europe  and  Asia.  When 
potato  vines  are  affected  there  is  a 
blackening  of  the  fibrovascular  sys- 
tem of  the  tuber,  and  eventually  a 
black  rot  may  set  in.  The  organism 
is  aerobic  and  an  alkaline  reaction 
is  produced.  No  gas  is  evolved, 
and  gelatin  is  not,  or  only  very 


FIG.  40.   SUBCULTURE  OF  BACILLUS    slightly,  liquefied.    Recently  it  has 
iDEsE  ON  AGAR  SLANT.    (Photo-    u          r        j   ,,        , -,  - 
graph  by  C.  O.  Townsend)  been  f°Und  that  thlS  organism  Pf°- 

duces  also  the  Granville  tobacco  wilt. 


XV.    BACILLUS:  OTHER  SPECIES 

• 

Among  other  disease-producing  organisms  of  this  genus  may 
be  mentioned  the  following : 

Bacillus  Hyacinthi-septicus  Heinz,1  causing  rapid  death  of  cul- 
tivated hyacinths. 

Bacillus  Cuboniamts  Macch.,2  said  to  be  the  cause  of  an 
important  leaf  and  twig  disease  of  the  mulberry,  especially  in 
France  and  Italy. 

1  Heinz,  A.    Zur  Kenntniss   der  Rotzkrankheiten  der  Pflanzen.     Centrbl.  f. 
Bakt.  u.  Parasitenk.  5  :  535-539.    1889. 

2  Macchiati,  L.    Sulla  biologia  del  Bacillus  Cubonianus,  sp.  nov.  Malpighia  5  : 
289-301.  //.  21,   1891. 


CHAPTER   X 

PHYCOMYCETES 

The  Phycomycetes  are  commonly  called  the  algal-like  fungi. 
They  are  very  diverse  both  with  reference  to  the  characteristics 
of  the  vegetative  and  of  the  reproductive  stages.  The  habits  of 
these  forms,  moreover,  are  so  varied  that  a  discussion  of  such 
peculiarities  may  be  postponed  until  the  individual  families  are 
described.  The  lower  forms  show  very  little  differentiation  or 
complexity  of  vegetative  parts,  and  the  fungous  body  may  indeed 
consist  of  a  single  simple  cell.  In  other  forms  the  fungous  body 
possesses  short  branches  or  thread-like  parts,  which  may  be  desig- 
nated hyphce.  In  the  higher  forms  there  is  a  well-developed  my- 
celium, or  system  of  branching  hyphae.  These  vegetative  hyphae 
are  commonly  siphonaceous  (nonseptate),  but  sometimes  cross 
walls  (septa)  are  produced.  In  fact,  there  are  families  in  which 
the  mycelium  is  constantly  siphonaceous  until  the  reproductive 
cells  are  cut  off,  and  cross  walls  occur  only  in  conjunction  with 
spore  development.  In  other  cases  the  hyphae  are  siphonaceous 
when  young,  becoming  generally  septate  with  age. 

The  methods  of  reproduction  are  either  by  means  of  nonsexual 
or  sexual  spores.  The  nonsexual  spores  are  produced  either  within 
differentiated  portions,  usually  tips  of  branches,  in  which  case  these 
differentiated  parts  are  termed  sporangia ;  or  the  spores  (conidia) 
may  be  produced  upon  hyphae,  in  which  case  the  latter  are  known 
as  conidiophores.  In  some  genera  the  conidia  also  become  spo- 
rangia germinating  by  the  production  of  motile  spores,  zoospores. 
Sexual  reproduction  by  the  union  of  differentiated  cells  (gametes) 
is  common  in  the  higher  forms  only,  and  the  gametes  may  be 
equal  or  unequal  in  size.  The  higher  forms,  however,  constitute 
the  majority  of  these  fungi. 

The  Phycomycetes  contain  seven  orders.  Two  of  these,  Ancy- 
listales  and  Monoblepharidales,  are  small  groups  of  water  fungi. 
One  order,  the  Mucorales,  is  an  unusually  interesting  group, 

'35 


136  FUNGOUS  DISEASES  OF  PLANTS 

composed,  however,  largely  of  saprophytic  organisms,  and  a  fourth 
order,  Entomophthorales,  contains  forms  which  are  for  the  most 
part  parasitic  upon  insects.  There  remain  therefore  three  orders 
which  are  important  from  the  standpoint  of  diseases  in  plants,  viz., 
Chytridiales,  Saprolegniales,  and  Peronosporales. 

I.    CHYTRIDIALES 

FARLOW,  W.  G.    The  Synchytria  of  the  United  States.    Bot.  Gaz.  10:  235- 

245.  pi.  4.    1885. 
HARPER,  R.  A.    Cell-Division  in  Sporangia  and  Asci.    Ann.  Bot.  13 :  467- 

525.  pis.  24-26. 
KUSANO,  S.    On  the  Cytology  of  Synchytrium.    Centrbl.  f.  Bakt,  Paras,  u. 

Inf.  19(Abt.  II):  538-543.  pi.  i.    1907. 
NOWAKOWSKI,  L.    Beitrag  z.  Kenntnis  d..  Chytridiaceen.    Cohn's  Beitrage  z. 

Biol.  d.  Pflanzen  Z:  73-100,  201-219.  pis.  4-6,  8-g.    1876. 
RYTZ,  WALTER.    Beitrage  zur  Kenntnis  der  Gattung  Synchytrium.    Centrbl. 

f.  Bakt,  Paras,  u.  Inf.  18  (Abt.  II):  635-655,  799-825.    1907. 
SCHROETER,  J.    Die   Pflanzenparasiten  aus  der  Gattung  Synchytrium.    Bei- 
trage z.  Biol.  d.  Pflanzen.  1  :    1-132.  pis.  i-j.    1870. 
SCHROETER,  J.     Chytridineae.     Pflanzenfamilien  (Engler   and    Prantl)  1  (i* 

Abt):    64-87.^^.^-77.    1892. 
ZOPF,  W.    Ueber  einige  niedere  Algenpilze.    1887.    Halle. 

In  a  consideration  which  might  include  several  hundred  fungi 
of  greatest  economic  importance,  as  disease-producing  organisms 
of  the  flowering  plants,  doubtless  no  mention  would  be  made  of 
the  above  order.  The  order  should,  however,  receive  at  least  casual 
attention  at  the  hands  of  the  student,  owing  to  the  important  posi- 
tion which  it  occupies  as  the  lowest  of  the  true  fungi.  It  is  a  strik- 
ing fact  that  a  considerable  majority  of  these  lower  fungi  are  parasitic 
upon  protozoa,  algae,  and  other  fungi.  Some,  however,  are  para- 
sitic upon  higher  plants. 

These  plants  are  all  very  simple,  and  there  is  no  member  of 
the  family  which  possesses  a  true  mycelium,  although  delicate 
branches  of  the  fungous  body  occur.  Reproduction  is  accom- 
plished by  means  of  motile  spores,  or  swarm  cells,  produced  in 
sporangia.  In  higher  forms  cell  fusions  occur.  It  is  not  certain 
what  these  fusions  denote. 

II.  SYNCHYTRIACE^ 

In  this  family  are  included  the  majority  of  the  Chytridiales 
parasitic  upon  higher  plants.  They  occur  for  the  most  part  only 


PHYCOMYCETES 


137 


upon  plants  growing  in  moist  situations.  A  motile  spore,  zoo- 
spore,  comes  to  rest  upon  an  epidermal  cell,  and  penetration 
doubtless  results  after  a  minute  perforation  is  made,  by  the 
streaming  through  of  the  protoplasmic  body.  There  are  no  evi- 
dences of  a  mycelium.  The  presence  of  the  parasite  in  the 
epidermal  cell  may  in  time  cause  a  minute  gall-like  abnormality 
of  the  host.  The  small  galls  are  sometimes  so  numerous  as  to 
give  the  host  the  appearance  of  being  affected  by  a  rust  fungus. 


FIG.  41.    SYNCHYTRIUM  ON  PUERARIA,  STAGES  IN  THE  FOR- 
MATION   OF    THE    POLYNUCLEATE    FUNGOUS    BODY    AND    THE 

.     LYSIGENOUS  CAVITY.    (After  Kusano) 

The  simple  protoplasmic  mass  resulting  from  the  growth  of  the 
penetrating  swarm  spore  becomes  either  a  fruit  body,  sorus,  or 
a  resting  spore ;  in  the  latter  case  it  becomes  a  fruit  body  ulti- 
mately, and  this,  at  maturity,  breaks  up  into  numerous  sporangia, 
and  may  therefore  be  termed  a  sorus,  each  sporangium  eventually 
producing  swarm  cells. 

Harper  has  studied  from  a  cytological  point  of  view  the  de- 
velopment of  Synchytriuni  decipiens  Farl.,  and  from  this  study 
may  be  distinguished  seven  more  or  less  distinct  stages  in  the 
life  cycle  of  this  organism:  (i)  after  the  swarm  spore  comes  to 


138  FUNGOUS  DISEASES  OF  PLANTS 

rest  and  penetrates  the  epidermal  cell  of  the  host  there  is  con- 
siderable growth  in  this  single  cell  of  the  fungous,  vegetative 
body ;  (2)  multiplication  of  the  nuclei  in  the  vegetative  body  until 
a  considerable  number  is  formed ;  (3)  progressive  cleavage  in  the 
multinucleate  body  from  the  surface  inward,  such  that  uninu- 
cleate  bodies  (termed  protospores)  are  produced,  accompanied 
with  marked  shrinkage  of  the  segments ;  (4)  growth,  increase 
in  size  of  the  protospores,  followed  by  nuclear  divisions ;  (5)  the 
development  of  cell  walls  about  the  multinucleate  spores,  food 
storage,  and  passage  into  a  ripened  or  resting  condition ;  (6) 
germination  by  the  production  of  a  sporangium  from  each  multi- 
nucleate  spore,  each  sporangium  producing  a  number  —  usually 
eight  to  twelve  —  of  the  uninucleate,  uniciliate  spores  ;  (7)  the 
active  motile  stage. 

In  a  recent  study  Kusano  reports  that  a  Synchytrium  on  Pueraria, 
and  also  Synchytrium  decipiens,  affect  only  nonchlorophyllous  cells 
of  the  mesophyll.  In  each  he  finds  that  the  cell  wall  of  the  affected 
cell  (and  in  time  of  neighboring  cells)  is  dissolved.  Eventually  con- 
siderable lysigenic  cavities  are  formed  in  which  the  fungous  body 
lies  "encased  by  the  symplast  of  the  host"  (Fig.  41). 

Synchytrium.  In  this  genus  the  fruit  body,  upon  reaching 
maturity,  forms  no  highly  resistant  cell  wall  about  itself,  but  by 
immediate  differentiation  of  the  protoplasmic  contents  becomes 
the  sporangial  sorus. 

Pycnochytrium.  The  fruit  body  is  a  thick-walled  resting  spore, 
which  after  a  period  of  inactivity  germinates  by  the  protrusion  of 
its  contents  in  the  form  of  a  thin-walled  sporangial  sorus.  The 
sporangia  produce  uniciliate  swarm  spores. 

III.    CRANBERRY  GALL 
Synchytrium  Vacdnii  Thomas 

HALSTED,  B.  D.    Some  Fungous   Diseases  of  the  Cranberry.    N.  J.  Exp. 

Sta.  Built.  64:    1-40.  figs.  1-18.    1889. 
SHEAR,  C.  L.    Cranberry  Diseases.    Bureau  Plant  Industry,  U.  S.  Dept.  Agl. 

Built.  110:    1-64.  pis.  7-7.    1907. 

It  attacks  young  stems  and  leaves  as  well  as  flowers  and  fruit. 
The  small  galls,  reddish  in  color,  are  produced  on  the  surfaces  of 
the  parts  affected  in  great  numbers.  The  fungous  body  consists 


PHYCOMYCETES  139 

of  a  cell  (Fig.  42),   which  becomes  a  spore,  or  properly  a  spo- 
rangium, producing  upon  germination  a  mass  of  swarm  spores. 
These   spores,    being    dependent    upon 
abundant    moisture    for    their   distribu- 
tion,  may   be    rendered    more    or    less 
ineffective   by  withholding  water  from 
the  cranberry  plants  during  the  winter. 
This    fungus    also   occurs    upon    other 
ericaceous   plants   more   or   less  closely    FlG.  42.  BLACKBERRY  GALL: 
related  to  the  cultivated  cranberry.  RESTING  SPORE  STAGE 

IV.  PYCNOCHYTRIUM   GLOBOSUM  (Schroet.)  Schroet. 

This  is  a  parasite  common  in  Europe  and  America  on  many 
families  of  flowering  plants.  In  the  United  States  it  has  been 
found  on  plants  growing  in  the  peat  bogs  of  the  eastern  states, 
some  of  the  hosts  observed  being  a  species  of  violet,  wild  straw- 
berry, blackberry,  and  maple  seedlings.  It  causes  the  development 
of  small  but  noticeable  yellow  or  reddish  galls. 

The  entrance  of  the  swarm  spore  into  an  epidermal  cell  is,  as 
indicated  above,  followed  by  general  growth  of  the  protoplasmic 
mass.  The  affected  epidermal  cell  may  become  somewhat  in- 
vaginated,  but  the  enlargement  due  to  the  growth  of  the  fungous 
cell  within  is  such  as  to  give  the  appearance  of  a  minute  gall. 
The  resting  spore  is  shown  in  Fig.  42  as  it  appears  in  mid- 
summer. Later  there  results,  as  indicated,  the  sporangial  sorus, 
each  sporangium  of  which,  upon  germination,  produces  the  char- 
acteristic uniciliated  swarm  spores. 

V.  CHYTRIDIALES:  OTHER  SPECIES 

Among  other  Synchytriaceae  more  or  less-  commonly  found  in 
the  United  States  are  Synchytriiim  decipiens  Farl.  on  the  hog 
peanut,  Amphicarpa  monoica ;  Synchytrium  fidgens  Schroet.  on 
the  evening  primrose,  CEnothera  biennis ;  Pycnochytrium  aureum 
(Schroet.)  Schroet.  occurring  upon  numerous  hosts  ;  and  Pycno- 
chytrium Myosotidis  (Kiihn)  Schroet.  on  certain  Boraginaceae  and 
Rosaceae.  In  a  different  family,  Oochytriaceae,  may  be  included 
some  interesting  parasites  of  economic  plants.  These  fungi 


140  FUNGOUS  DISEASES  OF  PLANTS 

are  certain  members  of  the  genus  Urophlyctis.1' 2  Urophlyctis 
leproides  (Trabut)  Magn.  occurs  on  root  outgrowths  of  the  beet, 
Beta  vulgaris  ;  Urophlyctis  pulposa  (Wall.)  Schroet.  attacks 
leaves  and  stems  of  species  of  Chenopodium  and  Atriplex ; 
and  Urophlyctis  Alfalfa  (v.  Lagerh.)  Magn.  is  found  upon  the 
roots  of  alfalfa,  Medicago  sativa,  in  South  America  and  in 
Germany. 

VI.  SAPROLEGNIALES 

The  Saprolegniales  are  commonly  called  water  molds  on 
account  of  the  fact  that  the  majority  of  these  fungi  occur  in 
the  water,  usually  in  ponds  and  streams,  upon  dead  insects  and 
other  small  animals,  or  sometimes  upon  other  organic  matter. 
One  or  more  species  attack  fish,  producing  important  diseases. 
A  few  members  of  the  order,  however,  are  not  properly  water 
molds,  being  found  upon  plants  in  moist  places,  some  parasitic 
and  some  saprophytic.  In  the  aquatic  forms  there  is  a  con- 
siderably branched  mycelium,  habitually  without  septa,  except 
where  spore-producing  parts  are  cut  off.  The  hyphae  are  fre- 
quently of  large  diameter  and  readily  evident  to  the  unaided 
eye.  Nonsexual  spores  are  produced  in  terminal  sporangia. 
Upon  liberation  the  spores  usually  become  motile.  Sexual  repro- 
duction is  by  means  of  unequal  gametes,  produced  in  oogonia 
and  antheridia.  The  latter  are  sometimes  wanting;  moreover, 
when  present  there  are  cases  (certain  aquatic  forms)  where  they 
are  apparently  functionless. 

Pythiaceae.  The  Pythiaceae  include  such  members  of  the 
Saprolegniales  as  are  important  in  plant  pathological  study. 
The  family  has  some  characters  which  seem  to  indicate  that 
they  might  with  equal  propriety  be  placed  in  the  order  next 
discussed,  Peronosporales.  The  species  which  are  of  interest 
in  this  connection  are  those  which  cause  damping-off,  rot,  or 
somewhat  similar  diseases  in  seedlings,  or  in  delicate  plants. 
This  family  differs  from  the  remaining  coordinate  members  of 
the  order  in  the  complete  differentiation  of  the  sporangia  from 

1  Magnus,  P.    Ueber  eine   neue  unterirdisch  lebende  Art  der  Gattung  Uro- 
phlyctis.   Ber.  d.  deut.  hot.  Ges.  19  :   145-150.  //.  27.    1901. 

2  Magnus,  P.    Ueber  die  in   den  knolligen  Wurzelauswiichsen  der   Luzerne 
lebende  Urophlyctis.    Ber.  d.  deut.  bot.  Ges.  20  :  291-296.  pi.  15.   1902. 


PHYCOMYCETES  141 

the  general  vegetative  hyphae,  and  also  in  the  production  of 
other  nonsexual  spores,  conidia,  borne  upon  hyphae,  which 
spores  germinate  by  means  of  a  germ  tube,  and  not  by  the  pro- 
duction of  motile  spores.  The  antheridia  are  always  functional, 
and  the  process  of  fertilization  is  apparently  exactly  the  same  as 
in  the  majority  of  the  Peronosporales.  Pythium  and  Pythiacystis 
are  important  genera. 

VII.    A  DAMPING-OFF  FUNGUS 
Pythium  de  Baryanum  Hesse 

ATKINSON,  GEO.  F.    The  Potting  Bed  Fungus.    Cornell  Univ.  Agl.  Exp.  Sta. 

Built.  94:  234-247.  //. /.    1894. 

HESSE.  Pythium  de  Baryanum,  ein  Endophytischer  Schmarotzer.  1874.  Halle. 
MIYAKE,  K.  The  Fertilization  of  Pythium  de  Baryanum.  Ann.  Bot.  15 : 

653-667.  pi.  36.    1901. 
WARD,   H.  MARSHALL.     Observations  on  the    Genus    Pythium   (Pringsh.). 

Quart.  Journ.  Mic.  Sci.  23:  485-519.  pis.  34-36.    1883. 

Habitat  relations.  This  species  is,  perhaps,  from  an  economic 
point  of  view,  the  most  important  in  the  order.  It  is  very  com- 
mon in  greenhouse  and  garden  soil  both  in  Europe  and  America, 
and  it  is  a  cause  of  one  of  the  various  greenhouse  maladies  known 
as  damping-off  in  seedlings.  The  conditions  which  favor  the  de- 
velopment of  the  fungus  are  a  considerable  degree  of  warmth, 
abundant  moisture,  and  weakened  condition  of  the  seedlings.  It 
is  especially  common  when  the  plants  are  being  grown  in  a  very 
crowded  condition.  While  most  common  in  the  greenhouse,  it 
may  affect  the  crop  in  the  field  as  well.  This  fungus  infests  a 
variety  of  seedlings,  but  those  of  the  cress,  cucumber,  sunflower, 
and  others  are  particularly  susceptible.  White  clover,  several  cru- 
cifers,  corn  and  other  members  of  the  grass  family  are  likewise 
included  among  the  hosts. 

Symptoms.  The  effects  of  this  fungus  may  be  evident  upon 
the  seedlings  a  few  days  after  germination.  The  point  of  attack 
is  ordinarily  at  or  near  the  surface  of  the  ground.  The  tissues 
of  the  affected  region  promptly  lose  their  turgidity  and  usually 
appear  water  soaked  (Fig.  43).  When  the  tissues  collapse  the 
seedlings  fall  prostrate,  and  then  the  mycelium  invades  the  re- 
mainder of  the  plant,  if  the  latter  is  kept  moist  by  contact  with 
the  damp  soil. 


142 


FUNGOUS  DISEASES  OF  PLANTS 


FIG.  43.   BEAN  SEEDLINGS  ATTACKED  BY  PYTHIUM 
(Photograph  by  H.  H.  Whetzel) 

The  fungus.  The  mycelium,  like  that  of  most  Peronosporaceae, 
is  delicate,  more  or  less  variable  in  diameter,  and  much  branched. 
The  branches  are,  for  a  time,  at  least,  smaller  than  the  parent 
hyphae.  The  protoplasm  is  densely  granular  in  the  growing 


PHYCOMYCETES 


143 


portions.    The  hyphae  are  apparently  intercellular  at  first  and  after- 
wards intracellular. 

Terminal  or  intercalary  spherical  sporangia  are  sparingly  pro- 
duced. These  are  usually  persistent,  and  may  be  from  three  to 
five  times  the  diameter  of  the  hyphae.  During  germination  a 
short  tube  is  developed  at  one  side,  and  through  this  the  my- 
celium migrates,  forming  a  kind  of  swarm  sphere  within  which  it 
breaks  up  into  bean-shaped  masses,  which  are  set  free  as  zoospores 
with  two  lateral  (Hesse  figures  only  one)  cilia.  Thicker  walled 
sporangia-like  bodies,  called  conidia,  are  also  produced.  These 
are  deciduous,  and  germinate  immediately  by  forming  zoospores. 


\ 


FIG.  44.   MYCELIUM  OF  PYTHIUM  INVADING  TISSUES 

Thick-walled   resting  conidia  also  appear,   and  these  eventually 
germinate  by  means  of  a  germ  tube. 

The  oogonia,  or  egg-bearing  gametes,  are  formed  either  as 
terminal  or  intercalary  enlargements,  and  are  of  much  the  same 
form  as  the  sporangia.  When  two  or  three  times  the  size  of 
a  hypha  they  are  cut  off  from  the  vegetative  cells.  The"  proto- 
plasm is  gradually  differentiated  into  a  central  denser  portion, 
ooplasm,  or  oosphere,  and  a  less  dense  peripheral  "  peri  plasm." 
A  coincident  development  of  an  antheridium  or  male  gamete 
takes  place,  the  latter  arising  either  as  the  enlarged  terminal 
portion  of  a  separate  antheridial  branch  (from  the  same  or  from 
a  different  hypha),  or  as  a  lateral  cell  cut  off  directly  adjacent 
to  the  oogonium.  More  than  one  antheridium  may  be  present, 
each  coming  in  contact  with  the  oogonium.  From  an  anther- 
idium a  fertilization  tube  grows  into  the  oosphere,  and  through 
this  tube  a  nucleus  and  some  cytoplasm  pass  in,  and  the  nucleus 
fuses  with  the  nucleus  of  the  oosphere  (Fig.  45).  This  process 


144 


FUNGOUS  DISEASES  OF  PLANTS 


FIG.  45.    SEXUAL  REPRODUCTION  IN  PYTHIUM 
(a,  after  Miyake) 


has  been  carefully  studied,  and  the  evidence  must  be  accepted. 
Subsequently,  a  thick  wall  forms  about  the  oosphere,  which  now 
properly  becomes  the  mature  egg,  or  oospore, 
measuring  ordinarily  25-35/1  in  diameter. 
The  development  of  an  oospore  may  be  com- 
pleted, under  favor- 
able conditions,  in 
a  single  day. 

Since  this  fungus 
may  readily  con- 
tinue its  growth 
into  dead  tissues  it 
may  be  cultivated 
indefinitely  in  Van 
Tieghem  cells  or  in 
specially  devised  cul- 
ture chambers,  and 
the  various  repro- 
ductive processes 
may  therefore  be  carefully  followed.  It  is  evident  that  with  care 
the  fungus  might  be  isolated  and  grown  in  pure  cultures.  The 
material  of  the  genus  Pythium  from  various  hosts  and  localities 
should  be  carefully  studied  and  compared  under  control  conditions, 
as  there  is  much  doubt  concerning  the  validity  of  species. 

VIII.    BROWN  ROT  OF  THE  LEMON 
Pythiacystis  Citrophthora  R.  E.  Smith 

SMITH,  R.  E.    A  New  Fungus  of  Economic  Importance.    Bot.  Gaz.  42:  215- 

221.  figs.  /-j>.    1906. 
SMITH,  R.  E.    The  Brown  Rot  of  the  Lemon.    Calif.  Agl.  Exp.  Sta.  Built. 

190:    1-70.  figs.  i-2g.    1907. 

Occurrence.  The  brown  rot  of  the  lemon  is  a  disease  which 
has  become  very  prominent  in  the  region  of  lemon  production 
in  California  during  the  past  few  years.  It  affects  more  or  less 
every  operation  having  to  do  with  lemon  production  and  market- 
ing, and  at  the  time  of  the  investigations  which  were  undertaken 
in  California  for  its  control  it  seemed  to  threaten  the  stability 
of  this  industry.  The  brown  rot  may  be  found  in  the  orchard, 


PHYCOMYCETES  145 

in  the  packing  house,  and  in  storage  conditions.  From  the 
description  subsequently  given  it  may  be  readily  distinguished 
from  forms  of  decay  due  to  common  mold  fungi.  It  is  most 
serious  in  connection  with  lemon  growing,  but  the  fungus  pro- 
ducing the  disease  may  also  affect  to  a  slight  extent  at  least  the 
orange,  pomelo,  and  other  citrous  fruits.  In  the  orchard  the  dis- 
ease may  be  found  upon"  fruit  which  has  fallen,  or  that  which 
is  hanging  very  close  to  the  moist  soil.  It  is  most  abundant 
during  wet  weather,  or  follow- 
ing irrigation,  and  is  therefore 
intensified  where  the  soils  are 
heavy.  It  is  estimated  that  under 
favorable  conditions  for  the  fun- 
gus a  box  of  lemons  per  tree 
is  no  extraordinary  loss. 

Symptoms.    The  first  indica- 
tions of  the  trouble  may  be  noted 
in  a  brownish  or  purplish  dis-        FIG.  46.   BROWN  ROT  OF  LEMON 
coloration  of  the  rind,  showing  <After  R"  K  Smith> 

light  on  the  greener  fruit,  and  darker  on  the  yellow  fruit.  Both 
young  and  old,  vigorous  and  weak  fruits  alike  are  affected,  and 
the  disease  is  particularly  characterized  by  a  marked  and  peculiar 
odor,  by  its  rapid  spread  from  fruit  to  fruit,  in  the  packing  house, 
or  while  stored  in  boxes,  and  by  the  presence  of  small  flies 
wherever  the  affected  fruit  is  stored  in  quantity.  After  storage 
for  a  week  or  ten  days  there  may  develop  upon  the  affected 
lemons  a  white  mold-like  growth  (Fig.  46),  and  frequently  upon 
such  affected  fruit  there  is  subsequently  produced  also  the  blue 
mold,  Penicillium.  The  blue  mold  alone,  however,  does  not 
spread  rapidly,  and  has  not  the  peculiar  odor  of  the  brown- 
rot  disease.  The  disease  may  appear  upon  fruit  in  storage, 
which  seemed  to  be  perfectly  colored  and  sound  when  passed 
by  the  washer. 

The  fungus.  The  fungus  concerned  in  the  production  of  this 
decay  is  apparently  one  which  was  unknown  until  attention  was 
directed  to  this  lemon  disease,  and  which,  while  it  is  an  active 
parasite  of  citrous  fruits,  it  is  doubtless  ordinarily  a  common  sapro- 
phyte found  in  moist  soils  and  in  water.  The  mycelium  of  this 


146 


FUNGOUS  DISEASES  OF  PLANTS 


fungus  penetrates  the  rind  and  other  fibrous  portions  of  the 
lemon  to  a  considerable  extent ;  it  is  much  branched,  irregular 
in  diameter,  and  extensive.  Upon  the  lemon,  as  a  rule,  no  form 
of  spore  is  produced,  but  there  is  developed  frequently  a  con- 
spicuous aerial  growth  due  to  the  emergence 
of  many  mycelial  branches.  In  some  cases 
these  are  produced  in  more  or  less  tuber- 
culate  masses.  Conidia  and  sporangia  appear 
under  favorable  conditions.  In  moist  soil  near 
affected  fruit  the  sporangia  are  developed 
abundantly  upon  a  fine  much-branched  my- 
celium (Fig.  47).  The  sporangia  measure 
20—60x30—90/1.  (averaging  35x50/4). 
They  are  lemon-shaped,  or  subspherical  with 
pronounced  apical  protuberance.  In  water 
FIG.  47.  SPORANGIA  OF  germination  is  effected  by  means  of  a  vari- 
able  number  of  zoospores,  often  about  thirty, 
each  biciliate  with  long  cilia  (Fig.  48). 
Control.  Ordinarily  the  fungus  does  not  produce  any  spore 
stage  upon  the  surface  of  the  lemon.  On  moist  soil,  however, 
it  produces  sporangia  and  sometimes  conidia. 
The  infection  of  the  fruit  usually  takes  place 
in  the  orchards,  and  also  subsequently  by 
direct  contact  and  also  by  the  operation  of 
washing.  It  has  been  found,  for  instance, 
that  if  uninfected  lemons  are  dipped  in  water 
in  which  diseased  ones  have  been  washed, 
infection  will  in  time  result  on  the  healthy 
fruit.  In  fact,  the  ordinary  wash  water  may 
itself  contain  a  large  number  of  germs  of 
this  fungus  and  it  may  also  live  more  or  less  JTIG>  4g.  GERMINATING 
permanently  in  the  machine  used  for  wash-  SPORANGIUM  OF  PYTHIA- 
ing  such  fruit.  The  remedy,  therefore,  for  CYSTIS.  (After  R.E.  Smith) 
such  conditions  is  very  simple  and  merely  consists  in  treating 
the  water  used  for  washing  purposes  with  some  aseptic  or  toxic 
agent.  The  most  practicable  method  which  has  been  devised  con- 
sists in  using  copper  sulfate,  formalin,  or  potassium  permanganate. 
In  using  formalin  one  part  of  the  reagent  to  ten  thousand  parts 


PHYCOMYCETES  147 

of  water  may  be  employed,  or  I  pint  to  1250  gallons  has  been 
sufficient  to  check  the  infection.  Permanganate  of  potash  is  rather 
a  mild  disinfectant  as  compared  with  formalin  and  it  is  necessary 
to  use  i  pound  to  625  gallons.  A  stronger  concentration  dis- 
colors slightly  and  the  former  strength  is  advised.  Copper  sulfate, 
which  is  both  a  cheap  and  effective  disinfectant,  may  be  used, 
of  about  the  same  strength  as  the  permanganate  of  potash.  Care 
should  be  taken  that  this  is  not  employed  in  a  very  much  more 
concentrated  form,  I  pound  to  250  gallons,  for  instance,  resulting  in 
injury  in  the  form  of  a  burn.  Unfortunately,  however,  this  substance 
attacks  the  arm  of  the  tank  and  is  therefore  less  desirable  than 
those  previously  referred  to.  A  higher  concentration  of  blue  stone 
is  needed  on  account  of  the  alkalinity  of  the  water  used.  In  dis- 
tilled water,  one  part  of  blue  stone  to  one  million  will  be  effective. 

IX.    PERONOSPORALES 

DE  BARY,  A.  Zur  Kenntnis  der  Peronosporeen.  Bot.  Zeit.  39:  521-530,  537- 

544,  553-563,  569-578,  585-595>  601-609,  617-625.  pL  5.    1881. 
FARLOW,  W.  G.    Enumeration  of  the  Peronosporeae  of  the  United  States. 

Bot.  Gaz.  8:  3°5-3l5,  327-337-    1883. 
LUSTNER,  G.    Untersuchungen  iiber  die  Peronospora-Epidemien  der  Jahre 

1905  und  1906.    Ber.  d.  Konigl.  Lehranstalt  fur  Wein-,  Obst-  und  Gar- 

tenbau,  Geisenheim  a/Rh.  (1906):  119-140. 
ROSTOWZEW,  S.  J.    Beitrage  zur  Kenntnis  der    Peronosporeen.     Flora  92 : 

405-430.  pi.  11-13.    i9°3- 
SCHROETER,  J.    Peronosporineae.    Pflanzenfamilien  (Engler  u.  Prantl)  1  (i* 

Abt):   108-119.  figs.  92-102.    1893. 
SWINGLE,  W.  T.    Some  Peronosporaceae  in  the  Herbarium  of  the  Division  of 

Vegetable  Pathology.   Journ.  Mycol.  7 :   109-130.    1892. 
WILSON,  G.  W.    Studies  in  North  American  Peronosporales.    I.  The  Genus 

Albugo.    Torrey  Bot.  Club  Built.  34:  61-84.    1907.    II.  Phytophthoreae 

and  Rhysotheceae.    Ibid.:   387-416. 

The  members  of  this  order  are  entirely  parasitic,  many  of 
the  species  causing  important  diseases  of  cultivated  plants.  The 
mycelium  is  well  developed,  siphonaceous,  and,  with  exceptions 
in  one  genus  (Phytophthora),  intercellular.  The  asexual  spores, 
which  may  in  general  be  termed  conidia,  are  produced  upon 
erect  conidiophores,  which  are  from  the  first,  or  which  ultimately 
become,  aerial.  The  conidiophores  may  be  simple  or  diversely 
branched.  The  conidia  germinate  either  by  means  of  a  germ 
tube  or  by  the  production  of  motile  spores,  zoospores ;  in  the 


148  FUNGOUS  DISEASES  OF  PLANTS 

latter  case  the  conidium  becomes  a  zoosporangium.  Oogonia 
and  antheridia  are  also  present,  and  these  are  produced  within 
the  tissues  of  the  host.  The  oospores  upon  germination  give 
rise  to  numerous  zoospores  or  to  a  single  germ  tube.  Some 
members  of  both  families  (Albuginaceae  and  Peronosporaceae)  of 
this  order  deserve  careful  study.  To  the  genus  Phytophthora  of 
the  Peronosporaceae  Pythium  and  Pythiacystis  are  perhaps  closely 
related. 

Albuginaceae.  In  this  family  the  conidia  are  borne  in  chains ; 
the  conidiophores  arise  in  the  form  of  large  cushions  which 
might  be  termed  sori.  They  are  developed  beneath  the  epi- 
dermis, but  the  latter  is  finally  ruptured,  and  the  conidia  are 
exposed.  The  oospore  germinates  by  the  production  of  zoo- 
spores.  There  is  one  genus,  Cystopus. 

Peronosporaceae.  The  members  of  this  family  are  distinguished 
from  the  preceding  largely  by  the  conidiophores,  which  are  from 
the  beginning  aerial.  The  conidia  are  also  produced  singly.  This 
is  properly  the  family  of  the  downy  mildews.  The  mycelium, 
which  is  commonly  intercellular,  develops  either  branched  or 
knob-like  haustoria.  The  oospore  germinates  by  means  of  a 
germ  tube. 

The  following  generic  key  includes  most  of  the  genera  together 
with  the  salient  generic  characteristics,  and  is,  in  this  family,  more 
practical  than  a  description  of  each  genus  : 

A.  Conidiophore  fully  developed  prior  to  the  formation  of  conidia. 

1.  Conidium  on  germination  becoming  a  swarm  sporangium  (zoo- 

sporangium).    Oospore  free  from  the  wall  of  the  oogonium. 
".'•';  •  .    '.  ''•"'»     .     .     .     .     Plasmopara 

2.  Conidium  becoming  a  swarm  sporangium,  conidiophore  short, 

irregular  in  form  and  diameter,  oospore  filling  oogonium,  with 
closely  adherent  walls.     ...     .     .     ,     ._  ..    .      Sclerospora 

3.  Conidium  germinating  by  means  of  a  germ  tube. 

a,  Conidium  provided  with  a  terminal  papilla  from  which 

the  germ  tube  proceeds.    Fertile  tips  arising  from  a 
disk-like  swelling Bremia 

b.  Conidium  without  papilla.    Fertile  tips  ordinarily  branch- 

like      Peronospora 

B.  Conidiophore   incomplete   when    first   conidia    produced.    Fertile  tips 

swelling  and  continuing  growth  as  successive  conidia  are  formed. 
.     .     . ,    Phytophthora 


PHYCOMYCETES  149 

X.   WHITE   "RUST"   OF   CRUCIFERS 
Cystopus  candidus  (Pers.)  Lev. 

DAVIS,  B.  M.    The  Fertilization  of  Albugo  Candida.    Bot.  Gaz.  29:   296-310. 

pi.  22.    1900. 
WAGER,  H.    On  the  Structure  and  Reproduction  of  Cystopus  candidus  LeV. 

Ann.  Bot.  10:   295-339.  pis.  25,  26.    1895.  m 
ZALEWSKI,  A.    Zur  Kenntniss  der  Gattung  Cystopus  LeV.    Bot.  Centrbl.  15  : 

215-224.    1883. 


FIG.  49.    FLOWERS  AND  PEDUNCLES  OF  RADISH  DEFORMED  BY  CYSTOPUS 
(Photograph  by  II.  H.  Whetzel) 

The  common  white  "rust"  of  cruciferous  plants  appears  to 
be  common  throughout  the  world.  The  fungus  is  frequently 
one  of  the  first  of  the  order  to  make  its  appearance  in  the  spring 
and  the  last  to  disappear  in  winter.  Evidently,  it  is  not  readily 
affected  by  minor  climatic  differences,  and  probably  slight  dews 
are  sufficient  to  insure  its  propagation. 

This  fungus  is  most  common  upon  the  forms  of  the  ubiqui- 
tous shepherd's  purse  (Caps  el  la  Bursa-pastoris] ;  but  it  is  also 
common  upon  the  radish  (Raphanus  sativus\  horse  radish 
(Cockle aria  Armoracia),  cress  (Brassica  oleracea),  turnip  (Bras- 
sica  Rapa\  mustard  (Brassica  nigra},  water  cress  (Radicula  Nas- 
turtium-aquaticum),  etc. 


150 


FUNGOUS  DISEASES  OF  PLANTS 


Symptoms.  The  effects  of  the  fungus  are  somewhat  various 
upon  the  different  hosts.  Upon  the  shepherd's  purse  the  stems 
are  enlarged  and  distorted,  while  no  unusual  malformations  of 
floral  organs  and  leaves  generally  occur.  On  the  radish  the  floral 
organs  may  be  strikingly  hypertrophied  (Fig.  49),  ovary  sacs 
greatly  enlarged,  stamens,  petals,  and  sepals  distended  and  some- 
times becoming  leaf -like.  Upon  nearly  all  hosts  the  porcelaneous 


FIG.  50.   CONIDIAL  STAGE,  FERTILIZATION,  AND  GERMINATING 
OOSPORE  OF  CYSTOPUS.    (b  and  c,  after  De  Bary) 

conidial  cushions,  characteristic  of  the  family  to  which  this  species 
belongs,  are  prominent. 

The  fungus.  The  conidial  cushions  occur  upon  leaves,  stems, 
and  floral  parts,  or  fruits.  On  the  majority  of  hosts,  such  as 
shepherd's  purse,  horse  radish,  etc.,  oospores  generally  occur  only 
in  the  stems,  yet  upon  some  other  hosts,  particularly  upon  certain 
mustards  in  the  western  United  States,  oospores  alone  are  com- 
mon. The  mycelium  is  considerable,  and  constantly  intercellular, 
with  abundant  knob-like  haustoria.  The  mycelium  develops  abun- 
dantly at  some  points  just  beneath  the  epidermis,  and  there  are 
produced  numerous  short,  erect,  basally  branched  conidiophores. 
The  latter  give  rise  to  simple  chains  of  spores  in  basipetal  suc- 
cession. These  are  usually  separated  one  from  another  by  slight 


PHYCOMYCETES 

beak-like  projections.  The  developing  cushions  break  the  epidermis 
and  the  mature  spores  are  set  free.  Fig.  50,  #,  shows  a  section 
through  a  conidial  cushion.  Under  favorable  conditions  germina- 
tion of  the  conidia  proceeds  promptly  and  each  conidium  becomes 
a  zoosporangium,  the  protoplasmic  contents  dividing  into  six  or 
more  parts  which  emerge  through 
an  opening  developed  either  ba- 
sally  or  terminally.  The  zoospores 
are  set  free  as  ovate  swarm  cells 
with  two  unequal  lateral  cilia. 
After  a  brief  motile  period  they 
come  to  rest,  become  invested 
with  a  cell  wall,  and  may  push 
out  a  germ  tube  in  a  few  hours. 

The  oospores  are  normally 
produced  later  than  the  conidia. 
The  oogonia  and  antheridia  de- 
velop in  the  intercellular  spaces, 
and  the  mode  of  formation  is  FIG.  51.  FERTILIZATION  IN  CYSTOPUS 
much  as  in  Pythium.  The  oogonia  < After  R  M'  Davis> 

are,  however,  in  this  case  larger,  measuring  from  50  to  60  p  in 
diameter.  There  are  numerous  nuclei  in  the  early  stages.  It  is 
generally  agreed  that  in  this  species  the  differentiation  of  the 
ooplasm  is  accompanied  by  a  migration  of  the  nuclei  to  a  pe- 
ripheral position  and  the  organization  of  a  central  body  termed 
a  coenocentrum.  A  nucleus  then  returns  from  this  nuclear  zone 
to  the  region  of  the  coenocentrum.  Preceding  the  latter,  however, 
it  is  held  that  one  karyokinetic  division  may  be  constantly  found. 
The  zone  of  the  now  disintegrating  nuclei  indicates  fairly  well  the 
line  of  differentiation  between  periplasm  and  ooplasm.  As  the 
antheridial  tube  penetrates,  a  cell  wall  begins  to  be  laid  down  be- 
tween ooplasm  and  periplasm.  Into  the  tube  of  the  antheridium 
a  single  antheridial  nucleus  migrates. 

Special  attention  is  called  to  the  fact  that  at  maturity  of  the 
egg  there  is  a  single  nucleus  in  each  gamete,  but  the  egg  is  also 
provided  with  a  coenocentrum.  Fertilization  proceeds  exactly  as 
in  Pythium,  and  during  the  nuclear  fusion  the  ccenocentrum 
promptly  disappears.  Fig.  5 1  shows  the  oosphere  with  developing 


FUNGOUS  DISEASES  OF  PLANTS 

wall,  the  remains  of  the  antheridium,  the  fusion  nuclei,  and 
the  ccenocentrum.  The  wall  of  the  mature  oospore  is  brown  in 
color  and  sculptured  in  a  characteristic  manner.  The  oospores 
are  35-40^  in  diameter.  It  is  believed  that  nuclear  division 
proceeds,  during  the  maturity  of  the  oospores,  until  about  thirty- 
two  nuclei  are  present,  and  it  has  been  suggested  that  each  of 
these  divides  twice  preceding  germination,  which  again  takes 
place  by'  the  formation  of  zoospores.  A  period  of  rest  is  invari- 
ably required  between  maturity  and  germination. 

XI.  CYSTOPUS:  OTHER   SPECIES 

Other  species  of  Cystopus  which  are  very  generally  distributed, 
occurring  on  common  hosts  of  the  garden  and  field,  are 

Cystopus  Tragopogonis  Pers.,  found  on  salsify  ( Tragopogon  por- 
rifolius]  and  various  other  Composite ; 

Cystopus  convolvulacearum  Otth.,  on  species  of  the  morning 
glory  and  sweet  potato  family,  Convolvulaceae  ; 

Cystopus  Bliti  (Biv.)  Lev.,  on  several  species  of  pigweed,  Ama- 
rantaceae.  The  oospores  of  this  species  are  often  very  abundant 
in  late  autumn ;  the  stems  and  flower  spikes  in  which  they  occur 
are  deformed  and  usually  purplish. 

XII.    DOWNY   MILDEW   OF  THE   GRAPE 
Plasmopara  Viticola  (B.  &  C.)  Berl.  &  De  Toni 

CORNU,  M.    Etudes  sur  les  Pe'ronospore'es.    [Observations  sur  le  Phylloxera 

et  sur  les  parasitaires  de  la  vigne.]  1:    101-184.     1881  ;  2:    1-91.  1882. 
FARLOW,  W.  G.    On  the  American  Grape-Vine  Mildew.    Built,  of  the  Bussey 

Institution  (1876):  415-425.   pis.  2-3. 
Report  on  Experiments  made  in  1 888  in  the  Treatment  of  the  Downy  Mildew 

and  Black  Rot  of  the  Grape  Vine.    Bot.  Div.,  U.  S.  Dept.  Agl.  Built.  10 : 

1-61.    1889. 
SCRIBNER,  F.  L.    The  Fungous  Diseases  of  the  Grape  Vine:    I.  The  Downy 

Mildew.    Bot.  Div.,  U.  S.  Dept.  Agl.  Built.  2  :  7-18.  pis.  i,  2,  4  (in  part). 

1886. 
VIALA,  P.    Mildiou.    Les  maladies  de  la  vigne  (Chap.  2):   57-155-  Pls-  2~3- 

figs.  20-46.    1893.    Montpellier  et  Paris. 

Occurrence.  The  downy  mildew  of  the  grape .  is  one  of  the 
most  important  disease-producing  organisms  among  the  Pero- 
nosporaceae.  The  fungus  seems  to  be  of  American  origin,  and 


PHYCOMYCETES 


153 


was  at  first  probably  more  or  less  confined  to  the  Mississippi 
Valley  and  states  to  the  eastward.  It  has  been  known  for  a 
long  time  as  a  pest  in  the  Middle  Atlantic  States,  -extending 
westward  to  the  Mississippi,  but  in  the  states  farther  to  the 


FIG.  52.   GRAPE  LEAF  WITH  EARLY  STAGE  OF  DOWNY  MILDEW 
(Photograph  by  H.  H.  Whetzel) 

northeast,  while  equally  common,  it  has  been  less  disastrous  in 
its  effects.  This  is  to  be  accounted  for  in  part  by  the  vigorous 
growth  of  the  vine  under  more  constant  rainfall ;  but  the  greater 
injury  farther  west  has  been  attributed  particularly  to  the  fact 
that  the  fungus  appears  earlier  in  the  season.  The  disease  was 


154 


FUNGOUS  DISEASES  OF  PLANTS 


not  known  on  the  Pacific  Slope  during  the  early  history  of 
grape-growing  in  that  region,  but  it  is  now  not  uncommon.  The 
fungus  was  apparently  introduced  into  Europe  from  America, 
and  it  became  a  serious  pest  within  a  very  short  time  after  it  was 
first  noted  in  that  country.  This  greater  injury  under  European 
conditions  had  been  predicted  by  Farlow  on  account  of  the  early 
spring  and  the  relatively  slight  growth  which  is  made  by  Vitis 
vinifera,  the  cultivated  grape  of  Europe. 

The  grape  mildew  has  been  found  abundantly  on  practically  all 
species  of  cultivated  or  wild  grapes,  that  is,  upon  such  species  as 
Vitis  cestivalis,  Vitis  cordifolia,  Vitis  Labrusca,  and  Vitis  vinifera. 
It  occurs,  therefore,  on  the  smooth-leaved  species  as  well  as  on 
those  possessing  a  downy  lower  surface,  and  there  are  few  varie- 
ties which  are  notably  resistant  under  all  conditions. 

This  fungus  attacks  practically  all  young  or  green  portions 
of  the  growing  vine,  —  leaves,  shoots,  and  berries.  The  vine  may, 
therefore,  under  conditions  favorable  for  the  development  of  the 
fungus,  show  the  disease  abundantly.  Under  ordinary  condi- 
tions, however,  it  is  largely  confined  to  the  leaves,  and  its  in- 
jurious action  consists  in  the  production  of  discolored  spots  which 
prevent  or  inhibit  normal  physiological  activities  (Fig.  52).  A 
slight  attack  of  this  fungus  may,  however,  cause  no  perceptible 
diminution  of  the  amount  of  the  grape  crop.  Under  ordinary 
circumstances  the  fungus  may  be  found  in  the  early  summer, 
particularly  if  the  season  is  moist,  and  it  may  reach  its  greatest 
intensity  during  August  or  as  late  as  September. 

Symptoms.  Upon  the  leaves  the  first  indications  of  the  disease 
are  indefinite  spots,  which  from  the  upper  surface  are  yellowish 
in  color  and  irregular  in  size  and  form.  Upon  the  lower  surface 
of  the  leaf  the  spots  are  not  so  evident,  but  almost  simultaneously 
with  the  spots  above,  the  sporophores  of  the  fungus  are  produced 
on  the  lower  surface.  Later  in  the  season  the  spots  may  turn 
brownish  above,  and  upon  some  varieties  of  grapes  they  may 
be  almost  brown  from  the  beginning,  finally  appearing  as  small, 
angular  brown  spots,  visible  on  both  surfaces  of  the  leaf.  It  is 
only  when  the  fungus  is  very  severe  that  the  leaf  dries  and  falls 
prematurely.  Upon  the  shoots  depressed  areas,  dark  in  color,  are 
produced,  and  these  therefore  bear  no  resemblance  to  anthracnose, 


PHVCOMYCETES 


155 


which  may  appear  upon  the  shoots,  as  subsequently  described. 
Commonly  the  fungus  is  found  upon  the  berries  only  when  the 
latter  are  young,  although  a  form  of  brown  rot,  sometimes  called 
gray  rot,  may  be  produced  by  this  fungus  when  the  berry  is  more 


FIG.  53.   PLASMOPARA  ON  GRAPE,    (b  and  d  after  Farlow) 

a,  mycelium ;  £,  mature  conidiophore  ;  c  and  d,  zoospore  and  oospore 

formation,  respectively 

than  two-thirds  grown  (see  illustration  facing  page  i).  Upon  Vitis 
cordifolia  the  fungus  may  fruit  so  abundantly  upon  the  young  berries 
as  to  completely  envelop  them  in  a  downy  mass  of  sporophores. 
Under  such  circumstances  the  berry  does  not  at  that  stage  show 
evidences  of  decay,  and  it  is  only  when  the  berries  are  older,  and 
in  other  species  nearly  full  grown,  that  the  fungus  produces  a 
true  decay.  When  the  disease  occurs  upon  the  young  fruits  the 
financial  losses  may  be  severe. 


156  FUNGOUS  DISEASES  OF  PLANTS 

The  fungus.  The  mycelium  is  abundant  in  the  intercellular 
spaces,  varying  in  diameter  from  8  to  1 2  /u,  but  frequently  it  is 
of  less  diameter  in  the  more  compact  tissue  of  Vitis  vinifera.  In 
the  leaves  the  fungous  hyphae  may  be  found  throughout  the  part 
affected,  except  in  the  woody  parts  of  the  bundles  of  the  veins  and 
in  the  stem.  They  occur  also  in  all  tissues  except  the  xylem.  The 
haustoria  are  of  the  characteristic  knob  shape.  The  hyphae  are 
somewhat  more  densely  assembled  in  the  vicinity  of  the  stomata, 
and  through  the  stomata  there  emerge  several  sporophores  (Fig. 
53),  each  becoming  constricted  in  its  passage  through  the  open- 
ing, but  subsequently  attaining  practically  normal  or  more  than 
normal  diameter,  therefore  often  showing  a  bulbous  base.  At 
maturity  they  are  irregularly  branched,  the  central  axis  giving 
rise  to  lateral  offshoots  and  sometimes  the  axis  itself  may  be 
lost,  due  to  the  preponderance  in  growth  of  the  branches.  The 
method  of  branching  and  sporangial  production  has  been  care- 
fully worked  out  by  Farlow,  according  to  whom  "  the  branches, 
which  are  few  in  number,  generally  from  four  to  eight,  are 
placed  alternately  on  the  upper  third  of  the  axis,  being  generally, 
but  not  always,  distichously  arranged.  Relatively  to  the  main  axis, 
they  are  all  short,  the  broadest  expansion  from  side  to  side  not 
being  usually  greater  than  .12  mm.  The  branches  are  furnished 
with  branchlets  of  a  second  and  third  order"  (Fig.  53,  b). 

In  this  species  germination  of  the  zoosporangia  takes  place 
in  water  in  about  one  and  one  quarter  hours.  The  process,  as 
summarized  from  Farlow's  careful  studies  of  this  phenomenon, 
is  about  as  follows  :  Spores  produced  during  the  night  and  put 
to  germinate  during  the  early  morning  on  slides  containing  a 
few  drops  of  water  show  first  at  the  end  of  an  hour  the  be- 
ginning of  segmentation  of  the  protoplasmic  contents,  each  seg- 
ment having  a  single  nucleus.  These  round  themselves  off  into 
oval  bodies,  which  are  massed  at  the  distal  end  of  the  sporan- 
gium, and  in  time  they  escape  by  dissolving  or  rupturing  the 
cell  wall.  The  zoospores  pass  out,  generally  one  at  a  time,  re- 
main quiescent  a  moment  in  becoming  free,  and  then  swim  off 
rapidly,  each  as  a  mature  zoospore,  provided  with  two  lateral  cilia, 
projecting  usually  anteriorly  and  posteriorly  (Fig.  53,  c).  In  gen- 
eral, the  zoospores  are  more  or  less  ovate,  but  the  form  in  the 


PHYCOMYCETES  157 

same  zoospore  may  undergo  considerable  change.  The  period  of 
activity  is,  as  a  rule,  from  fifteen  to  twenty  minutes,  at  the  end  of 
which  time  the  resting  condition  is  assumed  by  the  loss  of  cilia,  by 
becoming  spherical,  and  by  the  development  of  a  cell  wall ;  then 
follows  germination  by  means  of  a  germ  tube.  Germination  is 
effected  practically  irrespective  of  ordinary  conditions  of  light  and 
temperature. 

The  oospores  of  this  species  are  not  so  commonly  found  as 
the  conidiophores.  They  are  more  common,  apparently,  in  the 
northeastern  states  and  are  generally  found  upon  Vitis  czstivalis. 
They  are  commonly  present  during  late  September  and  always 
"  in  the  discolored,  shriveled  parts  of  the  leaves,  and  are  most 
abundant  just  inside  what  are  called  the  palisade  cells  of  the 
upper  surface."  The  formation  of  these  oospores  is  characteristic 
of  the  family;  that  is,  large  terminal  or  intercalary  swellings  of 
the  mycelium  are  cut  off  by  septa,  and  there  results  an  oogonhim. 
In  the  neighborhood  of  this  oogonium  there  may  be  produced 
one  or  more  smaller  antheridia.  The  subsequent  development 
of  these  two  structures,  the  fusion  phenomena,  and  the  develop- 
ment of  the  oospores  (Fig.  53,  d]  take  place  approximately  as 
described  for  Pythium  de  Baryanum  and  Cystopus  candidus. 
At  maturity  the  oospore  almost  completely  fills  the  original 
oogonium  wall,  and  the  wall  of  the  oospore  itself  is  comparatively 
smooth,  thick,  and  yellowish.  The  oospores  measure  about  30/4 
in  diameter.  For  the  study  of  the  oospores  dried  material  may 
be  teased  out  in  potassium  hydrate  solution,  or  it  may  be  neces- 
sary to  boil  the  material  in  this  solution,  afterward  neutralizing 
with  hydrochloric  acid.  The  oospores  are -set  free  by  the  disin- 
tegration of  the  tissues  of  the  leaf,  and  they  are  probably  impor- 
tant in  carrying  the  fungus  over  winter.  Nevertheless,  much  work 
needs  to  be  done  in  the  way  of  determining  to  what  extent  the 
oospores  are  necessary  in  the  annual  propagation  of  this  species. 

Control  measures.  In  the  control  of  this  fungus  Bordeaux 
mixture  is  most  effective,  and  it  is  only  during  very  moist 
seasons,  that  is,  where  it  is  difficult  to  keep  the  surfaces  of 
the  leaves  covered  with  the  preparation,  that  the  fungus  has 
been  able  to  gain  headway  in  spite  of  spraying  operations.  In 
this  connection  it  is  interesting  to  note  that  copper  fungicidal 


158  FUNGOUS  DISEASES  OF  PLANTS 

mixtures  first  came  into  use  in  the  treatment  of  downy  mildew 
of  the  grape.  The  experiments  of  Millardet  in  France  in  1881, 
and  subsequently,  led  promptly  to  the  perfection  of  Bordeaux 
mixture  as  a  fungicide. 


XIII.    DOWNY   MILDEW   OF  THE   CUCUMBER 
Plasmopara  cubensis  (B.  &  C.)  Humphrey 

CLINTON,  G.  P.  Downy  Mildew,  or  Blight,  Peronoplasmopara  cubensis  (B.  &  C.) 

Clint.,  of  Musk  Melons  and  Cucumbers.    Conn.  (New  Haven)  Agl.  Exp. 

Sta.  Kept.:  329-362.    pis.  29-31.    1904. 

FARLOW,  W.  G.    Notes  on  Fungi  i.   Bot.  Gaz.  14:   187-190.    1889. 
HUMPHREY,  J.  E.    The  Cucumber  Mildew.  —  Plasmopara  Cubensis  (B.  &  C.) 

Mass.  Agl.  Exp.  Sta.  Kept.  8:  210-212.    1890. 
SIRRINE,  F.  A.,  and  STEWART,  F.  C.    Spraying  Cucumbers  in  the  Season  of 

1898.    N.  Y.  Agl.  Exp.  Sta.  Built.  156:   376-396.  pis.  1-4.    1898. 
STEWART,  F.  C.    The  Downy  Mildew  of  the  Cucumber :  What  it  is  and  how 

to  prevent  it.    N.  Y.  Agl.  Exp.  Sta.  Built.  119  :   154-183.  pis.  1-4.   1897. 

Habitat  relations.  The  two  most  important  diseases  of  the 
cucumber,  or  indeed  of  the  commonly  cultivated  members  of 
the  gourd  family  in  this  country,  are  the  downy  mildew  and  the 
bacterial  wilt  disease.  It  has  been  definitely  ascertained  that  the 
Plasmopara  is  the  chief  cause  of  the  poor  crops  which  have 
prevailed  in  the  cucumber  districts  of  New  York  and  a  part 
of  New  Jersey  in  recent  years.  The  downy  mildew  of  the 
cucumber  has  an  interesting  though  brief  economic  history.  In 
1869  the  fungus  was  described  upon  a  wild  plant  found  in  Cuba. 
It  appears  that  this  fungus  was  not  again  reported  until  early  in 
the  spring  of  1889,  when  it  was  found  in  greenhouses  in  New 
Jersey,1  and  by  the  end  of  the  season  it  had  been  detected  upon 
the  cucumber,  squash,  and  pumpkin  in  the  field  in  several  loca- 
tions in  that  state.  It  was  further  reported  during  the  same  season 
from  several  southern  states.  Subsequently  it  developed  2  that  the 
fungus  had  been  found  in  Japan  early  in  the  same  year. 

This  disease-producing  organism  is  now  known  to  occur  in 
many  sections  of  the  eastern  and  southern  United  States,  but 
no  mention  of  its  occurrence  in  Europe  has  as  yet  come  to 
my  attention.  It  is  most  abundant  in  regions  which  have  long 

1  Halsted,  B.  D.   Peronospora  on  Cucumbers.    Bot,  Gaz.  14  :  149-150.    1889, 

2  Farlow,    Notes  on  Fungi,  /.  c. 


PHYCOMYCETES 


159 


been  devoted  to  the  cultivation  of  melons  or  of  cucumbers, 
especially  for  the  pickling  trade.  Nevertheless,  it  is  now  a  very 
constant  disease  in  greenhouse-grown  cucumbers. 

The  fungus  has  been  found  on  most  of  the  cultivated  species 
of  the  Cucurbitaceae,  or  gourd  family,  such  as  cucumbers,  musk- 
melons  or  watermelons,  squash, 
pumpkins,  gherkin,  and  also 
upon  the  star  cucumber,  Sicyos 
angulatus,  and  a  few  other  wild 
species. 

Symptoms  and  effects  of  the 
disease.  The  effect  of  this  dis- 
ease upon  the  host,  that  is, 
upon  the  cucumber,  have  been 
very  clearly  presented  by  Stew- 
art as  follows  : 


The  leaves  show  yellow  spots 
which  have  no  definite  outline.  If 
the  weather  is  warm  and  favorable 
for  the  disease,  these  spots  enlarge 
rapidly  and  run  together  so  that  the 
whole  leaf  becomes  yellow  and  soon 
dies  and  shrivels  like  a  leaf  killed 
by  frost.  If  the  weather  is  cool,  the 
yellow  spots  spread  less  rapidly.  In 
the  latter  case  the  central  portion  of 
the  yellow  spots  becomes  dead  and 
brittle  and  of  a  light-brown  color. 
.  .  .  The  disease  invariably  begins 
with  the  oldest  leaves  and  proceeds 
toward  the  tips  of  the  vines.  Hence  the  disease  appears  to  proceed  from  the 
center  of  a  hill  outward.  In  a  field  recently  attacked,  the  center  of  every 
hill  will  be  clearly  marked  by  a  cluster  of  yellow  leaves,  so  that  the  rows  may 
be  plainly  seen  clear  across  the  field,  even  though  the  plants  are  large  and 
cover  the  ground.  Affected  plants  continue  to  grow  at  the  tips  and  put  out 
new  leaves,  and  it  is  interesting  to  note  how  the  disease  follows  at  a  distance 
of  about  four  or  five  leaves  behind  the  growing  tip.  After  the  disease  is 
once  thoroughly  established,  very  few  cucumbers  are  produced,  although  the 
plants  may  continue  to  flower  profusely.  The  few  cucumbers  which  are 
formed  grow  slowly  and  become  misshapen  so  that  they  are  unsaleable.  .  .  . 
Of  the  total  shortage  of  75  per  cent,  in  the  Long  Island  cucumber  crop  of  1896, 
it  is  safe  to  say  that  5  5  per  cent,  was  due  to  the  downy  mildew. 


FIG.  54.   PLASMOPARA  ON  CUCUMBER. 

SALIENT  PHASES  OF  CONIDIAL  CYCLE 

(After  G.  P.  Clinton) 


i6o 


FUNGOUS  DISEASES  OF  PLANTS 


The  fungus.  The  mycelium  of  this  fungus  is  typical  of  the 
family.  The  haustoria  have  very  much  the  form  of  those  pre- 
viously described  for  the  grape  mycelium.  The  sporophores  arise 

through  the  stomates, 
singly  or  in  small  clus- 
ters, and  they  are 
considerably  branched, 
somewhat  more  flexu- 
ous  than  those  of  the 
grape  mildew,  and  the 
fruiting  tips  are  less 
rigid  and  more  widely 
M  separated  one  from 

;^j  B    another,   corresponding 

more  nearly  to  separate 
branches.  The  spores 
or  zoosporangia  are 
slightly  violet  tinted  in 
mass  and  generally 
ovate  in  outline.  The 
germination  of  the  spore 
has  been  followed  care- 
fully and  is  known  to 
take  place  by  means  of 
the  characteristic  motile 
zoospores.  Clinton 
alone  has  illustrated  the 
various  stages  of  germi- 
nation (Fig.  54,  c  and  d\ 
FIG.  55.  PERONOSPORA  ON  YOUNG  CABBAGE  LEAF  Occasionally  the  normal 

sporophores  are  accompanied  by  short,  swollen  hyphae  (Fig.  54,  b), 
which  may  also  bear  spores.  It  is  believed  that  the  latter  are  pro- 
duced under  unfavorable  conditions,  and  similar  modifications  have 
been  noted  in  other  species.  The  oosporic  form  of  this  species  has 
not  yet  been  found,  and  it  is  doubtful  if  it  occurs  in  this  country. 

Control.  Very  careful  experiments  have  been  made  with  a  view 
to  holding  in  check  the  ravages  of  this  fungus,  and  it  has  been 
found  that  the  greater  part  of  the  damage  can  be  prevented  by 


PHYCOMYCETES  161 

properly  spraying  with  Bordeaux  mixture.  Seven  sprayings  in 
New  York  have  almost  invariably  enabled  growers  to  control  this 
disease.  The  5-5-50  formula  may  be  recommended. 

Plasmopara  Halstedii  Farl.  is  widely  distributed  in  the  United 
States,  where  it  is  found  on  various  members  of  the  Compositae, 
especially  sunflower  and  Jerusalem  artichoke,  Helianthus  annuus 
and  Helianthus  tuberosus,  species  of  Bidens,  etc. 

XIV.    SCLEROSPORA 

CUGINI,  G.,  and  TRAVERSO,  G.  B.  La  Sclerospora  macrospora  Sacc.  parasita 
della  Zea  Mays.  Le  Stazioni  speriment.  agrar.  italiane.  35  :  46-49. 

TRAVERSO,  G.  B.  Note  critiche  sopra  la  Sclerospora  parassite  di  Graminacee. 
Malpighia.  16:  280-290.  1902. 

There  are  perhaps  three  species  of  this  genus.  The  species 
which  has  been  apparently  most  widely  distributed  and  best 
known  is  Sclerospora  graminicola  (Sace.)  Schroet.  This  species 
occurs  upon  several  grasses,  especially  Setaria  spp.  The  leaves 
are  affected,  and  in  severe  attacks  they  may  be  considerably 
rolled  and  shredded.  The  conidiophores  are  relatively  evanes- 
cent. They  are  irregular  in  form  and  generally  nodulose,  or  of 
irregular  diameter,  generally  short,  branched,  and  slightly  colored 
with  conidia  i2-2oxio-i8/x.  The  oospores  are  at  first  densely 
granular  and  hyaline  in  appearance,  later  they  are  slightly  colored, 
thick-walled,  united  with  wall  of  oogonium,  and  angularly  glo- 
boidal,  usually  40-42  ft  in  diameter.  Another  important  species, 
Sclerospora  macrospora  Sacc.,  formerly  known  only  on  a  few  true 
grasses,  has  more  recently  been  found  to  be  the  cause  of  an  im- 
portant disease  of  corn  in  Italy.  The  tassel  is  the  chief  seat  of 
infection.  Fairchild  reports  this  fungus  from  the  United  States. 
In  this  species  conidiophores  are  unknown,  and  the  oospores  are 
about  60-65/4  in  diameter. 

XV.    DOWNY  MILDEW  OF  CRUCIFERS 
Peronospora  parasitica  (Pers.)  De  Bary 

WAGER,  HAROLD.  On  the  Fertilization  of  Peronospora  parasitica.  Ann. 
Bot.  14:  263-279.  pi.  26.  1900. 

This  fungus  seems  to  be  particularly  abundant  in  England,  but 
it  is  also  found  in  other  parts  of  Europe  and  in  the  United  States. 
Practically  all  cultivated  Cruciferse  are  more  or  less  subject  to  it, 


162 


FUNGOUS  DISEASES  OF  PLANTS 


as  well  as  many  wild  species.    It  frequently  causes  stem  deformi- 
ties, and  in  England  it  is  often  associated  with  Cystopus  candidus 

on  Capsella,  while  in  this 
country  it  is  perhaps  best 
known  as  a  pest  in  cauli- 
flower culture  under  glass, 
yet  occasionally  destructive 
in  cabbage  cultures  in  the 
open,  and  less  frequently 
occurring  on  radish,  turnip, 
etc. 

The  conidiophores,  shown 
in  Fig.  56,  a,  are  character- 
istic of  the  genus.  The  co- 
nidia  germinate  (Fig.  56,  b] 
from  one  side  by  means  of  a  germ  tube.  The  development  of  the 
oospores  of  this  species  has  been  carefully  studied  and  would 
correspond  closely  to  that  described  for  Cystopus  candidus  except 
that  in  this  Peronospora  there  is  no  true  ccenocentrum. 


FIG.  56.  PERONOSPORA  ON  CABBAGE 
CONIDIAL  STAGE 


XVI.    ONION   MILDEW 
Peronospora  Schleideniana  De  Bary 

THAXTER,  R.    The    Onion    Mildew.     Conn.  Agl.   Exp.  Sta.  Kept.  (1889): 

155-158. 

TRELEASE,  WM.  The  Onion  Mold.  Wis.  Agl.  Exp.  Sta.  Kept.  (1884):  38-44. 
WHETZEL,  H.  H.   Onion  Blight.  Cornell  Agl.  Exp.  Sta.  Built.  218  :    138-161. 
figs.  1-17.    1904. 

The  onion  mildew,  blight,  or  mold  is  a  disease  which  has 
been  recognized  for  more  than  half  a  century.  At  various  times 
since  1884  it  has  been  reported  as  of  consequence  in  parts  of 
the  United  States  from  New  England  to  Wisconsin.  It  is  proba- 
bly far  more  common  and  destructive  than  has  been  supposed,  as 
shown  by  the  observations  of  Whetzel  in  1903. 

The  disease,  in  the  regions  referred  to,  appears  in  late  June  or 
July,  and  in  the  early  morning  while  covered  with  dew  it  is  in 
young  stages  conspicuous  by  a  "  furry  violet  appearance  "  of  the 
affected  leaves.  Later  the  leaves  become  moldy  in  character,  pale, 
collapsed,  and  often  broken.  Fig.  57  shows  a  diseased  plant  in 


PHYCOMYCETES 


163 


an  acute    stage.    Older  onions  are  apparently  more   susceptible 
than  young,  and  recovery  in  the  former  case  is  seldom. 

The  fungus.    The  mycelium  is  considerable,  and  it  penetrates 
practically  all  parts  of  the  leaf.  The  minute  haustoria  are  numerous, 


FIG.  57.   ONION  MILDEW 
(Photograph     by     H.    H. 
Whetzel) 


FIG.  58.    MATURE  CONIDIOPHORE,  GERMINAT- 
ING  CONIDIUM,     AND     MYCELIUM     OF     ONION 

PERONOSPORA.    (c  after  Whetzel) 


thread-like,  and  often  branched  at  the  tip.  The  conidiophores 
arise  through  the  stomates.  They  are  of  the  characteristic  type, 
often  320/4  in  height,  and  bear  large  elliptical  conidia  (44-52  x 
2 2-26  fjb)  which  germinate  promptly  by  a  side  tube  and  effect 
penetration  through  the  stomates.  The  time  required  for  infec- 
tion and  the  production  of  conidiophores  again  is  extremely 


164  FUNGOUS  DISEASES  OF  PLANTS 

short,  so  that  the  fungus  spreads  with  great  rapidity.    Oospores 
are  commonly  produced. 

Control.  It  would  seem  that  this  fungus  has  been  controlled 
in  New  York  by  systematically  spraying  where  it  is  likely  to  be 
abundant  after  June  15.  In  addition,  however,  it  is  important  to 
destroy  the  tops  of  diseased  plants,  and  by  no  means  to  return 
these  to  the  land  or  throw  them  on  the  compost  heap,  since  the 
oospores  retain  their  vitality  a  long  time.  Rotation  of  crops  is 
also  important. 


XVII.  PERONOSPORA:  OTHER  SPECIES 

Peronospora  sparsa  Berk,  is  not  an  uncommon  parasite  of 
cultivated  roses  in  Europe.  At  times  it  has  been  productive 
of  serious  epidemics.  Affected  leaves  show  brown  spots  on  the 
upper  surfaces  not  unlike  the  blotches  produced  by  other  fungi, 
but  on  the  under  surfaces  the  repeatedly  dichotomous  conidio- 
phores  appear  in  sufficient  quantity  to  be  readily  recognized  as 
a  mildew. 

Peronospora  effusa  (Grev.)  Rabh.  develops  during  moist  weather 
a  destructive  disease  of  spinach  (Spinacia  oleracea),  and  it  is  also 
common  upon  other  members  of  the  Chenopodiaceae,  as  well  as 
upon  certain  Plantaginaceae.  Pale  or  water-soaked  spots  are  pro- 
duced and  the  leaves  may  be  rapidly  killed.  Ordinarily  oospores 
are  found  in  quantity. 


XVIII.    DOWNY  MILDEW  OF  THE  LETTUCE 
Bremia  Lactuca  Reg. 

Downy  mildew  of  the  lettuce  is  not  an  infrequent  pest  where 
lettuce  is  grown  under  glass  during  the  winter  and  spring.  It 
also  occurs  with  cool  weather  in  the  open,  particularly  upon  fall 
lettuce.  This  fungus  is  also  quite  generally  distributed  on  several 
species  of  Senecio,  Sonchus,  and  Lactuca  as  well  as  on  a  few 
other  species  of  Composite.  Upon  lettuce  the  conidiophores  of 
the  fungus  appear  on  the  under  side  of  the  leaf,  and  the  areas 
affected  are  at  first  merely  paler  in  color,  afterwards  wilting. 


PHYCOMYCETES 


165 


The  conidiophores  appear  singly.  They  are 
much  branched  and  near  the  apices  of  the 
branches  at  maturity  peculiar  disk-like  swellings 
are  produced,  each  of  which  originates  circum- 
ferentially  about  four  tentacular  tips  inclined  out- 
ward so  as  to  continue  more  or  less  the  general 
direction  of  the  branch  axis.  Ovate  conidia  meas- 
uring 16-22  x  1 5-20  p  are  produced  singly,  and 
these  germinate  readily  in  water,  emitting  a  germ 
tube  through  an  apically  developed  pore  (Fig.  59). 
Oospores  are  occasionally  found.  These  are  small, 
26—3  5  ft  in  diameter,  light  brown,  and  roughened. 
In  controlling  this  fungus  general  sanitary  pre- 
cautions must  be  taken  and  a  maximum  of  light 
and  ventilation  should  be  constantly  afforded. 


GERMI- 
CONID- 
BREMIA 


XIX.    THE  LATE  BLIGHT  AND  ROT  OF  THE  POTATO 
Phytophthora  infestans  (Mont)  De  Bary 

CLINTON,  G.  P.  Downy  Mildew,  or  Blight,  Phytophthora  infestans  (Mont.) 
De  By.,  of  Potatoes.  Conn.  (New  Haven)  Agl.  Exp.  Sta.  Kept.  (1904): 
363-384.  pis.  32-37.  Ibid.  (1905):  304-330.  pis.  23-25. 

DE  BARY,  A.  Recherches  sur  le  developpejnent  de  quelques  champignons 
parasites.  Ann.  d.  Sci.  Nat.  Bot.  20  (4me  Se>.):  1-148.  pis.  1-13. 
1876. 

DE  BARY,  A.  Researches  into  the  Nature  of  the  Potato  Fungus  —  Phytoph- 
thora infestans.  Journ.  Roy.  Agl.  Soc.  12  (2d  ser.):  240-269.  figs. 
1-8.  1876. 

JONES,  L.  R.    Certain  Potato  Diseases  and  their  Remedies.    Vt.  Agl.  Exp. 

Sta.  Built.  72:   13-16. 
(Short  accounts  also  in  several  earlier  bulletins  and  reports.) 

JONES,  L.  R.  Disease  Resistance  of  Potatoes.  Bureau  Plant  Ind.,  U.  S.  Dept. 
Agl.  Built.  87:  1-39.  1905. 

STEWART,  F.  C;  EUSTACE,  H.  J.,  and  SIRRINE,  F.  A.  Potato  Spraying  Experi- 
ments in  1906.  N.  Y.  Agl.  Exp.  Sta.  Built.  279:  154-229.  pis.  1-2. 
figs.  1-4.  1906.  (Cf.,  also,  Bullts.  290,  307,  and  311.) 

STUART,  WM.  Disease  Resistance  of  Potatoes.  Vt.  Agl.  Exp.  Sta.  Built.  122  : 
107-136.  1906. 

WARD,  H.  MARSHALL.  Diseases  of  Plants.  The  "  Potato  Disease,"  Chapt.  5  : 
59-85.  1896.  London. 

The  late  blight  and  rot  of  the  potato  is  so  generally  known 
that  frequently  this  malady  is  simply  called  the  "  potato  disease." 
From  an  economic  point  of  view  it  is  the  oldest  potato  malady, 


166  FUNGOUS  DISEASES  OF  PLANTS 

and  it  has  been  the  cause  of  great  disaster  in  many  potato-growing 
regions  before  methods  for  its  control  were  well  known.  All  who 
are  familiar  with  the  history  of  potato  growing  doubtless  know  of 
the  potato  famine  of  1845.  The  serious  famine  in  Ireland  was  very 

largely  due  to  this  failure  of  the 
potato  crop,  a  failure  due  to  the 
prevalence  and  unusual  destruc- 
tiveness  of  the  Phytophthora. 

Distribution.  At  one  time  it 
was  the  current  opinion  that  this 
fungus  is  very  widely  distributed 
throughout  the  United  States, 
but  a  more  careful  study  of  po- 
tato diseases  has  shown  that  it  is 
very  largely  limited  to  New  Eng- 
land and  New  York,  extending 
also  into  the  potato-growing  re- 
gions of  Canada.  It  is  not  en- 
tirely absent  from  regions  much 
farther  south  and  west,  but  in 
such  districts  it  seldom  assumes 
any  importance.  In  Europe  it 
is  widely  distributed  and  may 
be  disastrous  throughout  Great 
FIG.  60.  PHYTOPHTHORA  ON  POTATO  Britain  as  wen  as  east  and  west 
LEAVES.  (Photograph  by  F.  C.  Stewart)  , 

from  Russia  to  trance,  extend- 
ing even  as  far  south  as  Italy.  The  distribution  of  this  fungus  and 
its  importance  as  a  disease  organism  are  entirely  dependent  upon 
climatic  conditions.  It  has  been  shown  that  it  becomes  of  seri- 
ous importance  only  when  favored  by  warm,  moist  weather.  As 
a  rule,  the  fungus  does  not  appear  in  the  northeastern  United 
States  prior  to  the  last  days  of  July,  and  it  is  most  abundant 
during  August  and  early  September.  A  few  days  of  rainy 
weather  suffice  to  give  it  a  start  and  to  bring  to  fruiting  the 
conidial  stage  on  the  leaves.  The  distribution  of  the  fungus 
is  then  accomplished  with  alarming  rapidity,  and  whole  fields 
may  be  devastated  within  a  period  covering  only  a  few  days 
of  such  weather.  While  it  is  generally  stated  that  warm  weather 


PHYCOMYCETES 


I67 


is  required,  it  has  also  been  shown  that  the  high  temperature  of 
summer  quickly  checks  its  spread. 

Symptoms.  Upon  the  leaves  of  the  potato  this  fungus  de- 
velops characteristic  spots  which  cannot  be  easily  confused  with 
other  potato  diseases.  These  spots  frequently  begin  at  the  edge 
or  tip  and  spread  until  the  whole  leaf  may  be  involved.  They 
present  in  moist  weather  a  dark, 
somewhat  water-soaked  appear- 
ance with  slightly  purplish  tint 
(Fig.  60).  In  drier  weather  they 
are  brown  without  the  definite 
markings  of  the  early  blight. 
The  moist  appearance  of  the 
spots  accompanied  by  the  wilt- 
ing of  the  leaf,  or  of  that  por- 
tion affected,  offers  an  easy 
diagnosis.  Generally  there  is 
no  accompanying  stem  injury, 
but  in  some  cases  the  trouble 
may  extend  to  the  stem ;  or, 
again,  it  may  be  found  upon 
the  leaves  as  an  extension  of  a 
stem  affection.  Upon  the  tubers 
this  fungus  develops  the  well- 
known  dry  rot  (Fig.  6l).  On  FIG.  61.  THE  PHYTOPHTHORA  DISEASE 

account  of  the  presence  of  the  OF   POTATO   TuBERS'    (Photograph  by 
,.  .....  r  F.  C.  Stewart) 

mycelium  within  the  tissues  of 

the  tuber  the  cells  are  killed  and  the  tubers  rendered  liable  to 
the  ordinary  forms  of  wet  rot  induced  by  bacterial  action  or  by 
mold  fungi.  The  dry  rot  may  cause  serious  damage  in  the  field, 
yet  this  damage  may  be  further  emphasized  or  even  first  made 
evident  while  the  potatoes  are  in  storage.  In  regions  which  are 
favorable  no  fungous  disease  may  become  more  quickly  disastrous, 
particularly  when  it  affects  the  tubers  as  well  as  the  vines.  Fortu- 
nately it  is  now  feasible  to  prevent  the  disease  and  possible  even 
to  stamp  it  out. 

Host  resistance.     For   more   than   half  a  century  the   resist- 
ance of  varieties  of  potatoes  to  the  late  blight  has  received  the 


1 68  FUNGOUS   DISEASES  OF  PLANTS 

attention  of  scientists.  The  early  work  was  remarkable  for  its 
time,  but  the  actual  results  accomplished  lose  their  value  now 
on  account  of  the  fact  that  the  older  varieties  have  largely  dis- 
appeared from  cultivation.  Excellent  work  was  done  during  the 
early  part  of  1870-1880,  when  Charles  Darwin  himself  became 
much  interested  in  resistance  breeding,  1872-1878.  As  a  result 
of  the  interest  which  was  then  established,  the  various  wild 
species  of  potato  growing  in  South  America  were  carefully  studied 
with  reference  to  this  point  and  numerous  crosses  and  selections 
made.  Again,  during  the  past  ten  years  there  has  been  a  re- 
vival of  interest  kvthas  subject,  and  to-day  the  general  problem 
is  better  understood  and  the  results  will  probably  be  more  lasting. 
It  may  be  said,  however,  that  while  many  varieties  have  been  de- 
veloped which  show  a  considerable  degree  of  resistance,  yet  it  is 
also  true  that  no  variety  may  be  expected  to  maintain  such  resist- 
ance throughout  a  long  period  of  time.  Gradually  there  will  be 
deviation  from  the  original  sort,  and,  moreover,  its  relation  to  the 
particular  environments  in  which  grown  will  doubtless  also  affect 
the  relations  to  the  blight  organism. 

It  cannot  be  expected  that  a  single  variety  will  be  equally  re- 
sistant under  different  conditions.  Therefore,  in  diverse  localities 
and  particularly  in  different  regions  variations  will  be  apparent. 
The  studies  which  have  thus  far  been  made  upon  resistance  have 
concerned  both  foliage  and  tuber  resistance.  According  to  the 
experiments  in  Vermont  (Stuart)  Rust  Proof  was  most  resistant 
in  1903,  so  far  as  the  foliage  is  concerned,  and  the  Dakota  Red 
was  second ;  while  in  1904  the  order  was  as  follows :  Monterey, 
Solatium  Commersonii,  Solatium  polyadenium,  Rust  Proof,  Sut- 
ton's  Discovery,  June,  Mexican,  Mammoth  Gem,  and  Manum's 
No.  3.  With  relation  to  tuber  resistance  Dakota  Red  has  made 
the  best  showing  for  two  seasons,  although  it  was  not  wholly  free 
from  rot.  The  other  varieties  which  show  least  blighting  of  the 
foliage  were  also  resistant  to  the  rot.  The  following  interesting 
summary  has  been  drawn  : 

1.  Some  varieties  are  less  subject  to  vine  injury  than  others. 

2.  Some  show  a  greater  tuber  resistance  to  rot  than  others. 

3.  With  some  there  seems  to  be  a  fairly  close  relation  between 
resistance  of  vine  to  disease  and  of  the  tuber  to  rot. 


PHYCOMYCETES 


169 


4.  Selection  has  not  given  visible  increase  of  resistance. 

5.  Hybridization  and  the  growing  of  seedling  plants,  followed 
by  careful  selection,  seem  to  offer  a  more  logical  method  of  se- 
curing disease-resistant  varieties  than  does  selection. 

The  tomato  is  occasionally  subject  to  this  disease,  but  so  far  as 
is  now  known  it  is  not  seriously  affected  in  any  part  of  the  world. 
-  The  fungus.  The  mycelium 
of  the  Phytophthora,  like  that 
of  the  other  members  of  this 
family,  is  unicellular,  and  the 
haustoria  are  filamentous.  The 
conidiophores  arise  singly  or  in 
groups  of  from  two  to  four 
from  the  stomates.  The  conidio- 
phore  is  branched,  and  at  the 
tip  of  each  branch  a  conidium 
is  produced.  The  conidium  is 
pushed  to  one  side  and  the 
branch  continues.  The  continua- 
tion is,  however,  larger  than  the 
tip  which  produced  the  conid- 
ium, so  that  this  further  growth 
is  marked  by  an  enlargement' 
of  the  branch,  making  a  very 
characteristic  form  of  conidio- 
phore  (Fig.  62).  The  conidia  are 
ovate  and  usually  measure  27- 
30  x  1 5-20  fji.  The  conidia  ger- 
minate readily  when  fresh,  by  the  FIG.  62.  SECTION  OF  POTATO  LEAF 
production  of  about  eight  zoo-  AND  CONIDIOPHORES  OF  THE  PHY- 
spores.  Germination  may  be  TOPHTHORA 

secured  in  water  but  apparently  not  in  nutrient  solutions.  The 
zoospores  are  motile  for  a  brief  time,  perhaps  seldom  longer 
than  a  hour.  They  then  come  to  rest  and  appear  spherical  and 
invested  with  a  wall.  Germination  readily  follows,  and  the  germ 
tube  penetrates  the  leaf  either  by  stomates  or  by  boring  through 
the  cuticle.  The  conidia  serve  not  only  to  spread  the  disease 
rapidly  from  leaf  to  leaf,  but  they  also  fall  upon  the  soil  and  may 


1 70  FUNGOUS  DISEASES  OF  PLANTS 

be  brought  in  contact  with  tubers.  They  penetrate  the  tubers  as 
readily  as  the  leaves,  the  dry  rot  being  produced  in  consequence. 
An  affected  tuber  which  does  not  show  the  disease  in  severe 
form  may  be  used  as  seed,  and  thus  the  disease  may  be  propa- 
gated from  year  to  year  through  the  seed  tubers.  It  is  now 
quite  certain  that  the  perennial  appearance  of  the  disease  is  due 
to  this  use  of  diseased  tubers.  It  is  not  always  possible,  how- 
ever, to  determine  if  the  mycelium  is  present  in  the  tubers,  since, 
even  though  they  may  have  been  stored  for  many  months,  the 


FIG.  63.   CONTROL  OF  LATE  BLIGHT  OF  POTATOES  BY  BORDEAUX  MIXTURE 
(Photograph  by  F.  C.  Stewart) 

fungus  will  not  develop  further  if  the  conditions  are  unfavorable. 
Thus  if  stored  at  a  low  temperature  and  in  a  dry  atmosphere  the 
rot  fungus  may  not  become  evident.  No  oosporic  stage  of  the 
Phytophthora  has  been  found,  and  it  is  believed  that  this  stage 
has  become  lost  and  is  now  wholly  unnecessary  in  the  life  cycle 
of  this  species.  (Recently  oospore-like  bodies  have  been  found.) 
Control.  Studies  looking  toward  the  prevention  of  the  potato 
blight  were  begun  during  the  middle  of  the  past  century.  At 
first  the  greatest  success  was  accomplished  only  in  securing 


PHYCOMYCETES  171 

comparatively  resistant  sorts.  Soon  after  the  discovery  of  Bordeaux 
mixture,  and  more  than  thirty  years  ago,  this  fungicide  was  effect- 
ively used  as  a  preventive  of  the  late  blight.  By  repeated  experi- 
ments under  a  variety  of  conditions  it  has  now  been  abundantly 
shown  that  the  proper  use  of  Bordeaux  mixture  will,  in  ordinary 
seasons,  hold  this  disease  in  check,  reducing  its  ravages  to  a  small 
minimum  (compare  Fig.  63).  It  is  ordinarily  advisable  to  begin 
spraying  with  5-5-50  Bordeaux  when  the  plants  are  about  six 
inches  high,  and  at  least  three  thorough  applications  from  ten  days 
to  two  weeks  apart  are  advised.  In  some  cases  two  additional 
applications  may  be  necessary.  Again,  it  should  be  remembered 
that  the  fungus  is  carried  over  winter  largely,  or  perhaps  entirely, 
by  a  hibernating  mycelium  in  the  tubers,  and  that  every  effort 
should  be  used  to  secure  seed  potatoes  from  a  field  in  which  no 
blight  or  rot  has  occurred.  If  this  latter  could  be  done  in  connec- 
tion with  a  system  of  rotation,  there  is  no  apparent  reason  why 
the  disease  might  not  be  practically  stamped  out  in  any  con- 
siderable region. 

XX.    DOWNY  MILDEW  OF  LIMA  BEANS 
Phytophthora  Phaseoli  Thaxt. 

CLINTON,  G.  P.    Downy  Mildew,  Phytophthora  Phaseoli  Thaxt.,  of   Lima 

Beans.    Conn.  Agl.  Exp.  Sta.  Rept.  (1905):  278-303.  pis.  20-22. 
HALSTED,  B.  D.    The  Downy  Mildew  of  Lima  Beans.    N.  J.  Agl.  Exp.  Sta. 

Built.  151:   18-24.  figs*  6-9-    1901. 
STURGIS,  W.  C.    The  Mildew  of  Lima  Beans  (Phytophthora  Phaseoli  Thaxt.). 

Conn.  Agl.  Exp.  Sta.  Rept.  (1897):   159-166.    (Also  Bot.  Gaz.  25:   191- 

194.    1898.) 
THAXTER,  R.   Mildew  of  Lima  Beans  (Phytophthora  Phaseoli  Thaxt).   Conn. 

Agl.  Exp.  Sta.  Rept.  (1889):   167-171. 

Occurrence.  Since  the  discovery  of  this  fungus,  in  1889,  near 
New  Haven,  Conn.,  it  has  been,  nearly  every  year,  of  sufficient 
importance  to  merit  special  attention  in  some  one  or  more  of  the 
North  Atlantic  States,  and  it  is  also  reported  from  Russia.  It  is 
found  upon  dwarf  and  pole  sorts  of  the  lima  bean,  Phaseolus 
lunatus,  and  has  been  reported  on  no  other  host.  The  fungus  is 
more  commonly  observed  upon  the  pods,  but  it  also  attacks  buds, 
leaves,  and  shoots.  Upon  the  pods  conspicuous  patches  of  the  white 
conidiophores  are  produced,  mostly  on  the  side  least  protected 


172 


FUNGOUS  DISEASES  OF  PLANTS 


by  the  vine.  Pods  badly  affected  may  wilt  and  die,  and  the  fungus 
may  penetrate  to  the  seed. 

Moist  seasons  are  most  favorable  to  the  production  and  spread 
of  this  disease.  Sturgis  has  determined  an  interesting  relation  of 
this  fungus  to  insects.  Bees  and  other  insects  visiting  the  blos- 
soms of  the  beans  may  come  in  contact  with  the  basal  portion 
of  the  style  and  the  basal  portion  of  the  ovary,  corresponding  to 
the  two  ends  of  the  pod.  Observation  indicates  that  it  is  at  these 
points  primarily  that  the  fungus  begins  its  work.  Rain  is  also 
effective  in  rapidly  spreading  the  spores. 

The  fungus.  The  mycelium  is  irregular  in  diameter,  siphon- 
aceous  when  young,  and  often  empty  and  septate  when  old.  The 
conidiophores  are  produced  in  great  numbers.  They  are  upright, 
considerably  branched  near  the  bases  and  longer  than  those  of 
other  species  of  the  genus.  They  form  on  the  surface  a  matted 
mass,  and  it  is  possible  that  threads  of  the  mycelium  proper  may 
also  develop  superficially.  The  conidia,  produced  much  as  in  the 
previous  species,  are  large,  measuring  generally  28-42  x  17-27/1, 
with  a  distinct  germinal  papilla.  Fresh  spores  germinate  readily, 
and  generally  by  the  production  of  biciliate,  fusiform  zoospores. 
Germination  may  also  occasionally  proceed  by  means  of  a  germ  tube. 

Oospores  of  this  fungus  were  not  found  until  1905.  According 
to  Clinton,  "  Judging  from  the  experience  of  the  past  year,  the 
oospores  should  be  looked  for  toward  the  end  of  the  season  and 
in  the  seeds  of  the  pods  badly  infected  with  the  mildew."  It  is 
believed  that  the  production  of  oospores  is  frequently  interfered 
with  by  the  rapid  growth  of  saprophytic  fungi.  The  oogonia  are 
inter-  or  intra-cellular,  rather  thick- walled,  smooth,  and  generally 
19. 5-22. 5  //,  in  diameter. 

By  carefully  removing  the  seeds  from  infected  pods,  Clinton 
was  able  to  grow  this  fungus  in  pure  cultures  on  such  seeds,  and 
likewise  on  nutrient  media  containing  agar,  corn  meal,  etc.  Both 
conidia  and  oogonia  were  produced. 

Control.  On  a  small,  scale  spraying  experiments  with  Bordeaux 
mixture  have  been  successful.  It  is  important,  however,  that  only 
seed  from  clean  pods  should  be  used.  Rotation  of  crops  is  required 
wherever  oospores  are  produced,  and  under  such  circumstances, 
also,  the  destruction  of  all  diseased  parts  is  equally  valuable. 


PHYCOMYCETES  173 

Phytophthora  cactorum  (Leb.  &  Cohn)  Schroet.  This  species 
of  Phytophthora,  if  it  is  a  single  species,  shows  as  great  a  range 
of  host  plants  as  the  common  damping-off  fungus,  Pythium  de 
Baryamnn.  It  was  first  described  as  a  disease  of  certain  Cactaceae 
grown  under  greenhouse  conditions,  also  of  succulent  species  be- 
longing to  the  genus  Sempervivum.  Hartig1  and  other  forest 
botanists  have  found  it  to  be  one  of  the  most  disastrous  fungi 
known  upon  seedlings  of  such  trees  as  the  pine  (Pinus),  beech 
(Fagus),  and  many  others.  Additional  hosts  among  herbaceous 
plants  have  also  been  well  established,  and  the  fungus  may  be 
regarded  as  unusually  widespread  and  important.  The  conidia 
(zoosporangia)  are  unusually  large,  often  averaging  60 /u-  in  di- 
ameter. Upon  germination  numerous  zoospores  are  produced. 
Oospores  are  present  in  this  species.  These  are  small,  often 
24-30/4. 

1  Hartig,  R.  Der  Buchenkeimlingspilz,  Phytophthora  Fagi,  m.  Unters.  a.  d. 
forstbot.  Institut,  Miinchen.  1  :  33-57.  pi- 3-  1880. 


CHAPTER  XI 

ASCOMYCETES 

The  Ascomycetes,  the  largest  class  of  the  fungi,  containing 
approximately  half  of  all  the  described  species,  have  perhaps 
one  common  characteristic,  —  the  ascus,  or  spore  sac,  generally 
with  a  definite  number  of  spores  (ordinarily  eight).  The  ascus 
is  of  many  types  and  may  be  produced  in  a  variety  of  ways, 
sometimes  apparently  in  a  mariner  analogous  to  simple  spo- 
rangia ;  again,  it  may  be  formed  upon  the  surface  of,  or  within, 
more  or  less  complex  fruit  bodies.  The  fruit  bodies,  in  turn,  may 
be  within  or  upon  a  modified  mycelial  tissue,  termed  a  stroma.  In 
some  cases  the  fruit  body  and  asci  are  developed  after  cell  and 
nuclear  fusion  in  special  organs,  phenomena  indicating  sexuality. 
The  size,  form,  and  consistency  of  the  fruit  bodies  are  extremely 
diverse,  examples  of  these  diversities  being  well  borne  in  mind 
by  a  comparison  of  the  large  edible  morel  with  the  minute  fruit 
bodies  (perithecia)  of  the  lilac  mildew. 

Nonsexual,  or  conidial,  spore  forms  of  manifold  variety  are 
known,  and  a  single  species  may  possess  several  of  these  forms. 
In  general,  the  mycelium  is  considerable,  exposed  or  imbedded 
in  the  substratum,  septate,  and  relatively  thick- walled.  Some 
orders  contain  only  a  few  and  others  many  parasitic  species. 

As  usually  considered,  the  Ascomycetes  include  about  ten  orders 
and  more  than  sixty  families.  For  convenience,  two  subdivisions, 
with  rather  artificial  limitations,  may  be  recognized  in  this  class 
among  those  with  definite  fruit  bodies,  namely,  (i)  the  Dis- 
comycetes,  in  which  the  asci  are  produced  in  a  body  finally  open- 
ing more  or  less  as  a  cup-shaped  or  saucer-shaped  apothecium  ; 
and  (2)  the  Pyrenomycetes,  in  which  the  asci  are  developed 
within  a  perithecium,  or  an  enveloping  structure,  which  may  be 
entirely  closed,  or  open  by  a  relatively  small  mouth,  the  ostiolum. 


ASCOMYCETES  175 

The  families  of  the  Discomycetes  (or  discomycete-like  forms) 
which  are  here  of  interest  are  Exoascaceae,  Helotiaceae,  Mol- 
lisiaceae,  and  Phacidiaceae.  The  Pyrenomycetes  from  which  im- 
portant parasitic  representatives  have  been  selected  are  the 
Perisporiaceae,  Erysiphaceae,  Hypocreaceae,  Dothidiaceae,  Myco- 
spherellaceae,  Pleosporaceae,  Gnomoniaceae,  and  Diatrypaceae. 

I.   EXOASCACE^: 

ATKINSON,  G.  F.    Leaf  Curl  and  Plum  Pockets.    Cornell  Univ.  Agl.  Exp.  Sta. 

Built.  73:  319-355.  pis.  1-20.    1894. 
PATTERSON,  FLORA  W.   A  Study  of  North  Am.  Parasitic  Exoasceas.    Labs. 

Natural  Hist,  Univ.  of  Iowa  Built  3:  89-135.  pis.  1-4.    1895. 
RATHAY,  E.    Ueber  die  Hexenbesen  der  Kirschbaume  und  iiber  Exoascus 

Wiesneri  n.  sp.    Sitzber.  d.  kaisl.  Akademie  d.  Wiss.  83 :  267-288.  pis. 

1,2.    1881. 
ROBINSON,  B.   L.    Notes  on  the  Genus  Taphrina.    Ann.  Bot  1 :    163-176. 

1887. 
SADEBECK,  R.    Die  parasitischen  Exoasceen.    Eine  Monographic  (Arb.  d.  bot. 

Museums  zu  Hamburg).    1893. 
SADEBECK,  R.    Einige  neue  Beobachtungen  und  kritische  Bemerkungen  iiber 

d.  Exoascaceae.    Ber.  d.  deut.  bot  Ges.  13:   265-280.  pi.  21.    1895. 
SCHROETER,  J.    Exoascaceae.    Pflanzenfamilien  (Engler  u.  Prantl)  1  (i*  Abt): 

158-161.  fig.  ij6.    1894. 

The  Exoascaceae  are  parasitic  fungi  causing  slight  or  very 
marked  abnormalities  of  the  leaves,  fruits,  etc.,  of  a  variety  of 
plants,  mostly  woody  forms.  The  deformities  are  commonly  of 
the  nature  of  leaf  curls,  malformed  fruits  (such  as  plum  pockets), 
and  witches'  brooms.  Such  diseases  are  especially  common  among 
the  stone  fruits.  This  family  of  fungi  is  considered  by  many  to 
be  closely  related  to  the  lowest  Discomycetes.  In  the  Exoas- 
caceae, however,  the  asci  are  produced  on  the  surface  of  the  host, 
arising  directly  from  the  mycelium,  without  the  development  of 
a  distinct,  complex,  basal  structure,  or  hymenial  layer.  Each  ascus 
may  possess  a  stalk  cell  or  it  may  be  merely  cut  off  by  a  cross 
wall  from  a  hypha  growing  perpendicular  to  the  surface.  An 
ascus  usually  contains  eight  spores,  which  in  some  cases  bud  ex- 
tensively in  a  yeast-like  manner,  even  within  the  ascus. 

In  the  genus  Exoascus,  which  embraces  those  forms  of  greatest 
economic  importance  in  the  family,  there  are  almost  constantly 
eight  spores,  and  budding  seldom  occurs  prior  to  the  expulsion 
of  the  spores  from  the  ascus. 


176  FUNGOUS  DISEASES  OF  PLANTS 

II.    PEACH  LEAF  CURL 
Exoascus  deformans  (Berk.)  Fuckel 

DUGGAR,  B.  M.    Peach  Leaf  Curl.    Cornell  Agl.  Exp.  Sta.  Built.  164:   371- 

388.  figs.  66-72.    1899. 
PIERCE,  N.  B.    Peach  Leaf  Curl :   Its  Nature  and  Treatment.    Div.  Veg.  Path. . 

and  Phys.,  U.  S.  Dept  Agl.  Built.  20:    1-204.  pis.  1-30.    1900. 
SELBV,  A.  D.    Preliminary  Report  upon  Diseases  of  the  Peach.    Ohio  Agl. 

Exp.  Sta.  Built.  92 :   226-231.    1898. 
SELBY,  A.  D.    Variation  in  the  Amount  of  Leaf  Curl  of  the  Peach  (Exoascus 

deformans)  in  the   Light  of  Weather  Conditions.    Proc.  Assoc.   Prom. 

Agl.  Sci.,  Ann.  Meeting  20:  98-104.    1899. 

Peach  leaf  curl  (Krauselkrankhcit  in  Germany ;  Cloqiie  du 
pecker  in  France)  is  an  important  fungous  disease  affecting  par- 
ticularly the  leaves  and  tender  shoots  of  the  peach,  but  injuring 
likewise,  occasionally,  the  flowers  and  fruit. 

Distribution.  Attempts  to  determine  the  country  which  might 
be  regarded  as  the  original  home  of  this  fungus  have  proved 
wholly  futile.  Leaf  curl  is  now  a  more  or  less  common  disease 
in  nearly  all  peach-growing  regions  of  the  world.  In  North 
America  it  is  known  throughout  the  country,  at  least  east  and 
west,  and  from  northern  Canada  to  the  Gulf  of  Mexico ;  while 
in  South  America  it  has  also  been  reported  from  several  peach- 
growing  districts.  In  Europe  it  has  long  been  common,  having 
been  reported  in  England  as  early  as  1821,  and  it  is  disastrous 
in  many  sections  of  China  and  Japan.  This  disease  occurs  also 
in  southern  Africa,  and  from  the  Sahara  northward  in  Algeria. 
According  to  reports  it  prevailed  in  Australia  even  in  1856,  and 
it  has  proved  most  pernicious  to  peach-growing  interests  in  New 
Zealand.  In  general,  therefore,  this  disease  is  known  wherever 
peach  growing  is  practiced.  In  the  United  States  the  general 
regions  in  which  the  more  serious'  and  constant  injuries  have 
been  felt  are  apparently  two,  viz.,  the  region  of  the  Great  Lakes 
and  the  Pacific  Slope  region,  the  latter  including  also  districts  in 
central  and  northern  California. 

Climatic  relations.  Plant  pathologists  are  almost  unanimous  in 
the  assertion  that  this  fungous  disease  is  most  prevalent  and  most 
disastrous  when  the  spring  is  cold  and  damp.  Practical  orchardists 
likewise  concur  in  this  opinion.  Pierce  about  ten  years  ago  col- 
lected statistics  from  about  one  hundred  orchardists  bearing  upon 


ASCOMYC 


this  point.  Ninety-two  per  cen^beKeyed  Jtir~x  ~co  ppyg  s 
favorable  to  the  disease  ;  morar  tl^a^Seventy-five  believe^-  J^e  wet 
weather  also  to  be  a  factor.  fcix^nd  seventeen  per  pgftjif  respec- 
tively, expressed  opinions  opposing  the  view  that  cold  and  mois- 
ture are  influencing  factors.  The  memorable  leaf-curl  years  in 
New  York  and  Ohio,  1893,  1897,  and  1898,  were  preceded  by 


FIG.  64.   PEACH  LEAF  CURL 

cold  and  humid  conditions  during  April,  the  time  when  the  buds 
normally  start.  On  the  other  hand,  there  is  no  record  that  the 
peach  leaf  curl  has  ever  been  particularly  destructive  during  a 
warm  and  relatively  dry  spring.  So  firm  is  the  opinion  of  a  few 
of  the  practical  growers  as  to  this  climatic  relationship  that  they 
refuse  to  believe  anything  more  than  that  the  weather  is  the  direct 
cause  of  the  leaf  curl.  Moreover,  heavy  dews  appear  to  be  of  in- 
significant environmental  importance,  and  in  view  of  the  conditions 
developing  dew,  this  would  be  anticipated. 


178  FUNGOUS  DISEASES  OF  PLANTS 

Losses.  The  losses  from  leaf  curl  may  not  be  so  readily  esti- 
mated as  with  many  other  fungous  diseases,  for  the  injury  to  the 
fruit  is  usually  indirect,  through  the  loss  of  leaves  and  the  gener- 
ally impaired  vitality  of  the  tree.  Before  the  adoption  of  any 
rational  preventive  measures  the  losses  in  the  United  States  were 
estimated  at  about  three  million  dollars.  In  general,  heavy  losses 
in  the  South,  on  the  Atlantic  seaboard,  and  in  the  Southwest  are 
infrequent,  yet  occasionally  the  damage  is  severe ;  while  in  the 
two  regions  previously  mentioned  as  more  severely  visited,  the 
losses  are  more  nearly  annual,  and  the  entire  crop  may  occa- 
sionally be  destroyed. 

Symptoms.  The  idea  generally  prevails  that  the  leaf  curl  oc- 
curs only  upon  leaves  and  young  branches,  but  the  flowers  and 
young  fruit  are  likewise  subject  to  attack.  Since  in  the  latter  case 
the  deformations  are  less  conspicuous,  and  dropping  of  the  parts 
affected  is  more  prompt,  it  has  often  escaped  attention.  Leaves 
of  the  peach  affected  by  this  fungus  may  be  detected  as  soon  as 
the  leaf  buds  have  become  slightly  upfolded.  The  coloring  of  the 
young  leaves  is  somewhat  heightened,  and  as  they  unfold  a  curl- 
ing and  arching  of  the  blades  becomes  prominent.  The  distortion 
may  be  confined  to  a  small  area  on  one  leaf  as  one  extreme,  or  it 
may  occur  on  all  leaves  and  petioles,  as  well  as  on  the  young  stem 
which  bears  these  (Fig.  64).  As  the  leaves  mature  the  green  or 
reddish  color  is  lost  and  the  hypertrophied  areas  become  pale  or 
slightly  discolored.  Diseased  shoots  may  attain  more  than  twice 
their  normal  diameter  and  become  pale  in  color.  Further  changes 
in  the  external  appearance  have  been  noted  in  a  gray  or  mealy 
appearance  of  the  surface,  which  occurs  as  a  result  of  the  produc- 
tion of  the  fungus  superficially.  Later  the  affected  leaves  turn 
brown  and  are  finally  defoliated.  When  defoliation  is  extensive 
the  fruit  crop  will  either  be  lost  entirely  or  so  stunted  as  to  be  of 
little  value.  Under  favorable  conditions  a  new  crop  of  leaves  will 
be  promptly  developed,  but  there  is  little  or  no  evidence  that  this 
second  crop  of  leaves  may  be  affected  even  to  a  very  limited  ex- 
tent. Gummy  exudations  sometimes  appear  on  the  enlarged  twigs, 
particularly  when  the  enlargement  is  not  terminal.  In  case  the 
terminal  bud  is  not  affected  it  may  continue  to  grow  later  in  the 
season,  thus  leaving  the  injured  or  swollen  portion  at  the  base  of 


ASCOMYCETES    ,  179 

the  new  growth.  It  was  formerly  supposed  that  this  fungus  was 
very  largely  propagated  by  a  perennating  mycelium,  or  by  infec- 
tions resulting  during  the  summer  and  persisting  in  the  woody 
parts  until  the  following  season,  but  as  will  be  shown  later,  infec- 
tions must  generally  occur  as  the  buds  unfold.  The  percentage 
resulting  from  a  mycelium  remaining  alive  in  the  hypertrophied 
twigs  is  very  small.  The  badly  affected  twig  dies  and  the  my- 
celium with  it.  From  other  affected  twigs  diseased  leaf  buds  are 
seldom  produced  (Fig.  65). 


FIG.  65.   ONE  HEALTHY  AND  THREE  DISEASED  TWIGS  OF  PEACH;  THE 
CENTER  TWIGS  RECOVERED  FROM  THE  ATTACK 

Susceptibility  of  host  varieties.  There  is  a  great  difference  in 
the  susceptibility  of  different  varieties  under  similar  conditions. 
Moreover,  a  single  variety  may  show  a  difference  in  resistance 
when  grown  under  diverse  environmental  conditions.  A  list  of 
the  most  susceptible  varieties  in  New  York  would  not  correspond 
with  a  list  for  California.  Among  susceptible  varieties  in  the  far 
West  have  been  included  such  as  the  following :  Crawford's 
Early  and  Late,  Elberta  and  Salway,  Heath  King  and  Hale's 
Early,  Lovell,  Old  Mixon  Free,  etc. ;  while  for  Ohio,  Mountain 
Rose,  Old  Mixon,  Globe,  Elberta,  and  others  are  among  those 
most  affected, 


l8o  FUNGOUS  DISEASES  OF  PLANTS 

A  striking  correlation  seems  to  obtain  between  the  serration 
of  leaves  and  susceptibility  to  curl,  the  serrate  varieties  being 
very  slightly  susceptible  as  compared  with  those  which  have  the 
glands  of  the  leaves  reniform  or  globose.  Other  interesting  rela- 
tionships have  been  suggested. 

The  fungus.  While  the  leaf  curl  has  evidently  been  known 
in  England  as  a  peach  disease  since  1821  or  earlier,  the  fungus 
was  first  described  by  Berkeley  in  1857.  It  has  therefore  been 
known  to  botanists  for  half,  a  century.  Infection  takes  place  at 
the  time  of  the  opening  of  the  buds  (most  frequently),  but  it  may 
also  result  (occasionally)  by  the  growth  of  a  perennial  mycelium 
from  the  old  wood,  in  which  it  has  rested  over  winter,  into  the 
expanding  peach  buds.  According  to  Sadebeck,  the  mycelium 
winters  over  in  the  primary  cortex  and  medullary  tissues  of  the 
one-year-old  branches. 

In  order  to  examine  the  mycelium  to  the  best  advantage  a 
section  should  be  made  of  a  leaf  or  twig  before  the  fungus  has 
appeared  upon  the  surface.  The  distribution  of  the  mycelium 
within  the  host  tissues  may  then  be  more  easily  followed,  owing 
to  the  greater  protoplasmic  content.  A  microscopical  study  of 
hand  or  microtome  sections  indicates  that  the  intercellular  my- 
celium is  quite  generally  distributed  in  the  parenchyma  of  the 
leaf  and  in  the  cortex  of  the  young  stems.  Three  types  of  my- 
celium have  been  recognized  (Pierce),  and  these  may  be  detected 
in  leaf  or  in  shoot : 

1.  The   most  common   type   is   designated    vegetative  hypJicz. 
These  are  very  diverse,  both   in  the  diameter  of  the  tubes  and 
in  the  character  of  the  branching,  as  shown  in  Fig.  66,  b.    Ad- 
jacent cells  are  separated  by  peculiar  plate  septa. 

2.  The  second  class  of  hyphae  are  known  as  distributive  hyphce, 
and  these  are  in  the  main  composed  of  long  cells  of  more  or  less 
uniform  diameter,  coursing,  for  the  most  part,  parallel  to  the  stem 
axis,  and  they  are  found  abundantly  in  the  pith  or  beneath  the 
epidermal  cells  (Fig.  66,  c). 

3.  Fruiting  hyphce.    The  vegetative  hyphae  which  have  devel- 
oped beneath  the  epidermis  push  up  between  the  epidermal  cells, 
and  there  is  formed  between  the  upper  edges  of  the  epidermal 
cells,  and  also  between  the  epidermis  and  the  cuticle,  an  extensive 


ASCOMYCETES 


development  of  short,  modified  hyphal  cells  (Fig.  66,  d).  These 
are  properly  the  ascogenous  cells,  which  by  an  abundant  budding 
process  form  frequently  an  almost  continuous  layer  beneath  the 
cuticle.  The  asci  develop  from  these  ascogenous  cells,  as  upward 
prolongations,  pushing  through  the  cuticle,  while  the  original 
ascogenous  cell  is  finally  cut  off  by  a  cross  wall  as  a  stalk  or  foot 


FIG.  66.   EXOASCUS  ON  PEACH:  ASCI,  GERMINATING  SPORES,  AND  HYPH^E 
(b,  c,  and  d  after  Pierce) 

portion.  The  ascus  is  usually  somewhat  truncated  at  the  apex  and 
densely  filled  with  protoplasm.  It  may  measure  25-40  x  8-n/x 
(ave.  30-35  x  9-10).  As  a  rule  it  contains  at  maturity  eight 
spores,  although  the  number  may  vary  from  four  to  eight  (Fig. 
66,  a).  These  asci  often  arise  in  such  numbers  that  they  form  prac- 
tically a  continuous  palisade-like  layer  over  the  fruiting  surface. 

The  ascospores  may  bud  before  being  thrown  out  of  the  ascus, 
but  as  a  rule  the  spores  are  forcibly  ejected  from  the  ascus  at 
maturity.  Budding  results  in  the  successive  production  of  conidia, 


1 82  FUNGOUS  DISEASES  OF  PLANTS 

which  may  therefore  be  termed  primary,  secondary,  etc.  These 
conidia  may  be  propagated  for  some  time  in  beerwort.  On  the 
host  germination  may  proceed  normally,  that  is,  by  the  direct  pro- 
duction of  a  true  germ  tube  ;  moreover,  germination  rather  than 
budding  is  occasionally  observed  in  culture.  The  grayish  cast 
given  to  the  surface  of  the  leaf  is  due  to  the  numerous  asci,  and  a 
mealiness  may  become  evident  later  from  the  abundance  of  conidia. 

Infection.  Since,  as  shown  later,  the  disease  may  be  in  very 
large  part  prevented  by  spraying  prior  to  the  opening  of  the 
buds,  it  is  evident  that  infection  would  seem  to  result,  in  general, 
by  spores  or  conidia  which  have  been  caught  in  the  bud  scales, 
or,  at  any  rate,  which  were  adherent  to  the  buds  at  the  time  of 
opening.  It  is  therefore  believed  that  the  marked  effect  of  con- 
ditions upon  the  prevalence  of  the  leaf  curl  is  brought  about  in 
this  way  :  During  cold,  moist  weather  the  young  leaves  within 
the  bursting  buds  would  be  in  a  state  described  as  suffused  with 
water,  and  consequently  attended  by  lowered  vitality.  The  fungus 
would  therefore  gain  entrance  more  readily.  If,  however,  at  this 
time  the  bud  scales  were  well  covered  with  a  toxic  fungicide,  the 
germ  tubes  of  the  fungus  would  in  most  cases  fail  to  cause  infec- 
tion. Again,  the  effect  of  conditions  does  not  end  with  infection, 
and  it  is  well  known  that  the  extent  of  the  disease  upon  single 
leaves  or  shoots  is  greater  when  the  cold,  moist  weather  is  per- 
sistent. It  is,  therefore,  probable  that  the  spread  of  the  fungus 
throughout  an  infected  leaf  or  shoot  is  directly  assisted  by  the 
continuance  of  lessened  vitality  and  water  suffusion  as  growth 
progresses. 

Control.  Preventive  measures  for  the  leaf  curl  have  been  made 
a  subject  of  careful  investigation  throughout  many  years.  It  has 
finally  been  clearly  shown  that  a  thorough  application  of  a  fungi- 
cide, preferably  Bordeaux  mixture,  during  the  late  winter  or  early 
spring  just  prior  to  the  opening  of  the  buds,  may  prevent  from 
90  to  95  per  cent  or  more  of  the  infections.  I  do  not  believe 
that  subsequent  sprayings  are  of  any  importance  except  in  a  case 
where  the  early  spraying  has  been  omitted  ;  and  the  fungus  be- 
ing abundant,  it  is  desired  to  cover  up  all  parts  of  the  plant  with 
a  spray  so  that  the  spores  may  be  in  large  part  killed  as  they  are 
produced,  or  as  budding  is  attempted. 


ASCOMYCETES 

III.  PLUM  POCKETS 
Exoascus  Pruni  Fuckel 

This  fungus  is  the  cause  of  the  well-known  deformities  of 
the  domestic  plum,  Prunus  domestica,   and  it  is  very  generally 


FIG.  67.   PLUM  POCKETS  ON  CULTIVATED  PRUNUS.   (Photograph  by 
H.  H.  Whetzel) 

distributed  throughout  Europe  and  portions  of  the  United  States. 
The  etiology  and  general  life  history  is  not  sufficiently  different 
from  the  peach  leaf  curl  to  require  detailed  treatment,  but  the 


1 84  FUNGOUS  DISEASES   OF  PLANTS 

general  characteristics  of  the  abnormalities  and  special  peculiarities 
of  the  fungus  may  be  mentioned.  The  mycelium  attacks  the  fruit 
buds  and  causes  remarkable  hypertrophies  in  the  developing 
ovaries.  The  mesocarpic  tissue  is  invaded,  whereby  it  is  stimu- 
lated to  the  production  of  an  abundant  spongy  growth  and  the 
whole  form  of  the  plum  is  enlarged  and  distorted.  Apparently  the 
connection  of  the  stone  with  its  usual  source  of  nutrition  is  broken 
up  and  no  stone  is  developed,  or  else  only  a  rudimentary  structure. 
It  is  claimed  that  the  mycelium  is  perennial,  that  here  infection 
results  by  the  growth  of  this  mycelium  into  the  young  shoots  and 


FIG.  68.  WITCHES'  BROOM  ON  CHERRY,  PRODUCED  BY  EXOASCUS 
(Photograph  by  F.  C.  Stewart) 

ovaries  in  the  spring.  This  point  requires  further  investigation. 
As  in  the  case  of  the  peach  leaf  curl  fungus,  the  ascogenous  cells 
are  developed  beneath  the  cuticle  and  the  elongating  asci  rupture 
the  latter.  The  asci  are  densely  crowded  together  and  do  not  all 
mature  at  the  same  time.  In  general,  the  asci  are  30-60  x  7-12  p. 
Robinson  notes  a  certain  dimorphism  in  the  asci,  slender  ones 
measuring  43-60  x  5-5-7,  and  stout  forms  27-35  x  9-12/4.  In 
several  instances  I  have  attempted  to  inoculate  young  plums  with 
spore-bearing  material  received  from  farther  south,  but  such  experi- 
ments have  invariably  failed.  In  general,  a  study  of  infection  phe- 
nomena in  the  Exoascaceae  would  seem  to  be  of  much  interest. 


ASCOMYCETES  185 

IV.    WITCHES'  BROOM  OF  THE  CHERRY 
Exoascus  Cerasi  Fuckel 

This  fungus  is  very  common  on  both  Primus  avitim  and  Prumis 
Cerasus  in  Europe.  It  has  been  reported  infrequent  in  this  country. 
The  mycelium  attacks  the  branches,  and  the  stimulation  due  to  its 
presence  results  in  the  formation  of  numerous  twigs  somewhat  in 
the  form  of  a  loose  broom  (Fig.  68).  According  to  some  observers 
the  twigs  may  be  slightly  thickened,  although  others  claim  that 
there  is  no  abnormality  in  the  latter.  The  leaves  on  affected  twigs 
are  also  penetrated  by  the  mycelium  and  they  become  somewhat 
reddish  and  wrinkled  or  crumpled.  The  asci  develop  upon  the 
leaves,  and  measure,  according  to  Sadebeck,  35-50  x  7-io/z  (25— 
33  X  6-9  in  specimens  studied  by  Atkinson).  During  the  flowering 
period  of  Pnmus  Cerasus  the  witches'  brooms  are  very  conspicuous, 
since  the  broom  usually  bears  leaves  only. 

Prevention  in  this  case  requires  the  destruction  of  all  affected 
branches,  as  well,  probably,  as  a  thorough  spraying  about  the  time 
the  asci  are  mature,  and  a  subsequent  one  when  the  buds  swell 
the  following  spring. 

Of  the  many  other  species  of  Exoascus  the  majority  are  para- 
sitic upon  different  species  of  Prunus,  while  Alnus,  Populus,  Acer, 
./Esculus,  Carpinus,  Crataegus,  Pyrus,  Quercus,  Ulmus,  and  other 
plants  are  also  hosts. 

V.    HELOTIACE^: 

The  Helotiaceae  are  Discomycetes  of  which  the  fruiting  body  is 
a  distinct  apothecium  or  cup.  In  texture  these  fungi  may  vary 
from  wax-like  to  a  rather  tough  consistency.  The  body  is  at  first 
almost  spherical  and  nearly  or  quite  closed.  With  growth  and  dif- 
ferentiation it  opens  into  the  characteristic  cup,  sessile  or  supported 
by  a  stalk  varying  in  length  in  different  species.  The  sterile  tissue 
of  the  cup  is  pseudoparenchymatous.  The  cylindrical  asci  arise 
from  a  hyphal-like  hymenium,  and  each  ascus  contains  eight  spores. 
At  maturity  the  ascus  opens  at  the  apex  and  forcibly  ejects  the 
spores,  the  latter  being  hyaline,  diverse  in  form,  and  1-8  celled. 
Filamentous  paraphyses  are  present.  Sclerotinia  and  Dasyscypha 
may  be  mentioned  as  containing  parasitic  species. 


186  FUNGOUS  DISEASES  OF  PLANTS 

Of  the  twenty-five  genera  of  this  family,  the  genus  Sclerotinia 
includes  the  most  important  parasitic  species.  It  is  characterized 
particularly  by  the  fact  that  typically  the  fruit  body  arises  from  a 
sclerotium,  which  may  be  defined  as  a  compact  mass  of  hyphal  ele- 
ments, sometimes  distinctly  pseudoparenchymatous  or  sclerotial  in 
texture,  serving  commonly  as  a  resting  or  more  resistant  mycelial 
stage.  The  sclerotium  may  be  developed  upon  the  living  host  or  it 
may  form  after  the  death  of  the  diseased  structure.  The  apothe- 
cium  is  usually  borne  in  this  case  on  a  rather  long  stalk,  and  it  is 
smooth  and  more  or  less  brown  in  color.  The  cylindrical  asci 
bear  in  uniseriate  fashion  eight  usually  elliptical  spores.  Conidial 
and  chlamydosporic  stages  may  be  present. 

VI.    SCLEROTINIA 

DE  BARY,  A.    Ueber  einige  Sclerotinien  und  Sclerotinienkrankheiten.    Bot. 

Zeitg.  44:  377-387  (etseq.).    1886. 
WAKKER,  J.  H.    Ueber  die  Infection  der  Nahrpflanzen  durch  parasitische 

Peziza- (Sclerotinia-)  arten.    Bot.  Centrbl.  29  :   309-313,342-346.    1887. 
WORONIN,  M.  Ueber  die  Sclerotienkrankheiten  der  Vaccinieen-Beeren.  Mem. 

de  1'Acad.  imp.  de  Sci.  de  St.  Pe'tersbourg  36  (ser.  8):   1888. 

Many  species  of  Sclerotinia  produce  diseases  of  plants,  and 
although  several  species  have  been  carefully  studied,  there  is 
much  in  the  way  of  unconfirmed  data.  A  monographic  study 
of  the  genus  is  greatly  needed.  The  apothecial  or  perfect  stage 
is  not  developed,  as  a  rule,  until  the  mycelium,  or  a  sclerotium, 
has  undergone  a  period  of  rest.  In  several  cases  it  is  well  estab- 
lished that  the  conidial  stages  are  members  of  the  form  genus 
Monilia.  It  is  also  declared  that  other  species  include  Botrytis 
forms  in  their  life  cycles.  For  convenience  the  following  tentative 
classification  of  species  of  Sclerotinia  is  suggested  : 

1.  Species  comprising  in  their  life  cycle  not  only  apothecia,  but  also  a 
Monilia  stage,  that  is,  with  conidia  produced  in  chains,  the  latter  frequently 
separated  one  from  another  by  special  structural  devices. 

a.  Species  in  which  both  spore  forms  may  be  produced  upon  the  same  host ; 
such  as  Sclerotinia  fructigena,  S.  Vaccinii,  S.  Aucuparice,  S.  baccarum,  S. 
megalospora,  and  S.  Oxycocci. 

b.  Species  whose  life  cycles  are  not  complete  upon  a  single  host ;  Sclerotinia 
heteroica  and  S.  Rhododendri. 

2.  Species  which  may  embrace  a  form  of  Botrytis  as  a  conidial  stage ; 
Sclerotinia  Fuckeliana. 

3.  Species  in  which   no  conidial  stages  have  been  convincingly  demon- 
strated ;  Sclerotinia  Libertiana,  S.  Betulce,  and  6".  Trifoliorum. 


ASCOMYCETES 

VII.    BROWN  ROT  OF  STONE  FRUITS 
Sclerotinia  fructigena  (Pers.)  Schroet.1 

ADERHOLD,  RUD.    Ueber  eine  vermuthliche  zu  Monilia  fructigena  Pers.  ge- 

horige  Sclerotinia.    Ber.  d.  deut.  hot.  Ges.  22:   262-266.    1904. 
HUMPHREY,  J.  E.    On  Monilia  fructigena.    Bot.  Gaz.  18  :  85-93.  pi.  7.   1893. 
NORTON,  J.  B.  S.    Sclerotinia  fructigena.    Trans.  Acad.  Sci.  of  St.  Louis  12 : 

91-97.  pis.  1 8-2 1.    1902. 
QUAINTANCE,  A.  L.    The  Brown  Rot  of  Peaches,  Plums,  and  Other  Fruits. 

Ga.  Agl.  Exp.  Sta.  Built.  50:  237-269.  Jigs.  1-9.    1900. 
SMITH,  ERW.  F.    Peach  Blight,  Monilia  fructigena,  Pers.    Journ.  Myc.  5  : 

123-134.  pis.  3,  6. 
SORAUER,  P.    Erkrankungsfalle  durch  Monilia.    Zeitsch.  f.  Pflanzenkr.  9 : 

225-235.  pi.  4.    1899. 
WEHMER,  C.    Monilia  fructigena  Pers.  (=  Sclerotinia  fructigena  m.)  und  die 

Monilia  Krankheit  der  Obstbaume.   Ber.  der  Deut.  Bot.  Ges.  16 :  298- 

307.  pi.  1 8.    1898. 
WORONIN,  M.    Ueber  Sclerotinia  cinerea  und  Sclerotinia  fructigena.    Mdm. 

de  1'Acad.  imp.  d.  Sci.  de  St.  Pdtersbourg.    VIIIe-Sdr.  Phys.-Math.  Cl. 

10(5):   1-38.  pis.  1-6.    1899. 

The  fungus  causing  the  brown  rot  of  fruits  has  been  known 
botanically  for  half  a  century,  but  its  great  economic  importance 
has  only  been  appreciated  during  the  past  twenty  years.  It  is  now 
a  well-known  disease  wherever  the  peach  is  grown  throughout 
Europe  and  America.  The  conditions  under  which  great  injury 
results  are,  however,  not  general  in  all  the  countries  named ;  and 
therefore  it  may  be  very  destructive  one  year  and  of  relatively 
slight  importance  the  following  season.  Whether  warm  or  cool, 
moist  weather  is  favorable  to  the  spread  of  the  disease,  but  the 
muggy  weather  of  midsummer  is  particularly  disastrous  to  the 
stone-fruit  crop,  on  account  of  the  rapid  spread  of  the  disease 
under  such  conditions. 

1  Under  this  title  is  discussed  the  widespread  rot  of  stone  fruits.  Two  species 
of  Sclerotinia  may,  according  to  the  work  of  Woronin,  be  distinguished  as  caus- 
ing somewhat  different  types  of  disease;  these  species  are  Sclerotinia  fructigena 
and  Sclerotinia  cinerea.  It  is  claimed  that  there  are  no  observable  differences  in 
the  mycelium  of  the  two  species,  but  that  differences  are  evident  in  the  color  of 
the  spore  masses  and  in  the  susceptibility  of  hosts  to  the  two  forms.  In  Sclero- 
tinia fructigena  the  spores  are  described  as  light  brownish-yellow,  or  ochraceous, 
while  in  the  other  they  are  invariably  gray.  Moreover,  in  the  former  the  spores 
are  larger,  averaging  20.9  x  I2.i/*,  while  the  latter  average  12.1  x  8.8 fi.  Sclero- 
tinia cinerea  is  said  to  be  most  abundant  on  the  common  stone  fruits,  whereas 
Sclerotinia  fructigena  is  also  found  on  pomaceous  fruits.  The  above  view  does 
not  appear  to  be  that  generally  held  by  American  pathologists,  and  it  is  not  uni- 
formly accepted  in  Europe.  We  shall,  therefore,  use  the  name  Sclerotinia  fructi- 
gena to  designate  this  rot-disease  of  diverse  stone  fruits. 


1 88  FUNGOUS  DISEASES  OF  PLANTS 

Extent  of  losses.  The  years  when  the  greatest  injury  has  been 
reported  from  various  sections  of  this  country  are  as  follows  :  In 
1887  Dr.  Erwin  F.  Smith  reported  it  from  Maryland  and  Delaware. 
The  extent  of  the  injury  probably  resulted  in  a  shortage  of  the 
total  crop  estimated  at  800,000  baskets  of  peaches.  It  was  also 
very  abundant  in  1891  and  1893.  Again,  during  subsequent  years, 
it  has  been  of  considerable  importance  in  the  Delaware  and  Chesa- 
peake peninsula.  In  1897  an  almost  total  loss  of  the  crop  in 
Alabama  was  reported,  the  following  year  being  somewhat  less 
disastrous.  Quaintance  states  that  the  year  1900  was  the  worst  in 
the  history  of  commercial  peach  and  plum  growing  in  Georgia. 
He  estimated  the  loss  at  40  per  cent  of  the  total  crop.  This 
would  mean  a  loss  of  between  $500,000  and  $700,000  for  that 
state  alone. 

Symptoms.  The  name  brown  rot  has  long  been  applied  to  this 
disease,  and  it  is  the  one  in  most  common  use,  although  many 
others,  particularly  ripe  rot,  are  also  employed  in  some  sections. 
This  disease  affects  practically  all  stone  fruits  (Prunus  spp.),  very 
few  varieties  of  either  peach,  apricot,  nectarine,  plum,  or  cherry 
being  free  from  it  during  seasons  favorable  to  the  fungus.  The 
fruits  are  the  most  common  seat  of  injury,  but  other  vegetative  parts 
are  likewise  susceptible.  As  a  rule  the  fruits  are  apparently  most 
easily  attacked  after  they  have  become  half  grown,  arid  the  sus- 
ceptibility increases  from  this  time  to  ripening.  Fruits  in  clusters, 
under  which  conditions  moisture  would  be  held,  are  more  readily 
injured. 

The  disease  first  makes  itself  evident  as  a  small,  dark  brown, 
decayed  spot.  This  spot  increases  in  extent  until  the  whole  fruit 
is  infested,  but  there  is  at  first  no  diminution  in  size,  and  no  sunken 
area  develops.  Before  the  whole  fruit  has  become  decayed,  how- 
ever, evidences  of  a  superficial  development  of  the  conidia  of  the 
fungus  may  appear.  As  a  rule,  however,  the  fungus  develops  its 
spores  only  after  the  fruit  has  decayed  considerably.  The  fungus 
then  breaks  through  the  surface  in  the  form  of  small  tufts,  con- 
sisting of  masses  of  conidiophores  with  an  abundant  production 
of  conidia,  the  appearance  being  as  shown  in  Fig.  69. 

The  flowers  may  also  succumb,  and  that  is  more  commonly 
the  case  the  year  after  an  unusual  outbreak  of  the  disease,  due 


ASCOMYCETES 


189 


FIG.  69.   BROWN  ROT  OF  PLUM  :  MONILIA  STAGE 

generally  to  the  fact  that  the  old  mummied  fruits  remaining  on 
the  twigs  an  large  numbers  serve  to  cause  a  very  general  infection 
at  the  time  of  blossoming.  The  twigs  are  also  susceptible,  but  it  has 
been  quite  definitely  shown  that  infection  of  the  twigs  results  only 


190 


FUNGOUS  DISEASES  OF  PLANTS 


when  either  flowers  or  fruit  produced  on  the  twigs  have  already 
fallen  prey  to  the  disease.  In  other  words,  the  fungus  must  grow 
directly  from  the  fruit  or  blossom  into  the  young  twigs,  since  it 
cannot  readily  penetrate  the  epidermis  of  the  latter.  Inoculation 

of  the  fungus  into  cuts  on  the 
bark  will,  however,  also  result  in 
a  twig  infection.  The  effect  of 
the  fungus  upon  the  twig  is  to 
produce  a  blight,  the  twig  being 
completely  killed  as  the  disease 
progresses  (Fig.  70).  Peaches 
and  apricots  are  more  subject  to 
the  twig  blight  than  other  stone 
fruits. 

Mummied  fruits.  The  fruit 
which  has  decayed  may  fall  to 
the  ground  or  hang  upon  the 
trees,  gradually  shrinking  with 
evaporation  each  to  a  crumpled, 
dried  mass,  generally  known  as 
a  mummy.  These  mummied 
fruits  are  the  chief  source  of 
infection  the  following  season 
under  ordinary  conditions.  It 
has  been  determined  that  the 
spores  produced  one  summer 
may,  under  certain  conditions 
at  least,  live  over  until  the  fol- 
lowing spring.  Further,  the 
mycelium  within  the  mummied 
fruits  more  readily  lives  until 
conditions  favorable  for  growth 
the  following  season.  It  is  also  possible  that  the  spores  which 
have  been  blown  about  and  adhere  to  bud  scales,  etc.,  may  likewise 
cause  infection  the  following  year. 

Rot  in  market  fruit.  Not  only  is  this  fungus  a  cause  of  consid- 
erable loss  in  the  orchard,  but  it  also  affects  the  fruit  in  shipment 
or  on  the  market.  When  the  spores  are  abundant  in  the  orchard, 


FIG.  70.   APRICOT  TWIG  KILLED  BY 
THE  BROWN  ROT  FUNGUS 


ASCOMYCETES 


191 


every  fruit  having  perhaps  some  on  its  surface,  these  spores  may 
germinate,  under  favorable  conditions  in  transit,  and  cause  infec- 
tion of  the  fruit  in  bulk,  so  that  a  shipment  which  showed  great 
promise  as  it  left  the  orchard  may  reach  the  market  in  practically 
worthless  condition. 

Susceptibility  of  hosts.  No  very  extensive  data  have  been  ac- 
cumulated with  reference  to  the  resistance  or  susceptibility  of  the 
many  varieties  of  stone  fruits  in  different  sections  of  the  country. 
In  general,  however,  it 
would  appear  that  among 
peaches  the  sorts  densely 
covered  with  hairs  or  down, 
such  as  the  Alexander,  Hill's 
Chili,  and  Triumph,  are  un- 
usually susceptible.  Among 
the  more  resistant  sorts  are 
to  be  found  the  Carman, 
Early  Crawford,  Elberta, 
Chinese  Cling,  and  some 
others.  Among  the  plums 
the  Japanese  varieties  suffer 
generally  in  most  sections 
of  the  country.  The  Amer- 
ican group  of  plums  is  also  FlG-  71-  SECTION  OF  PEACH  TWIG  AFFECTED 
..  .  WITH  THE  MONILIA.  (After  Erw.  F.  Smith) 

susceptible,  and  apparently 

more  susceptible  at  the  South  than  farther  north.  The  Wild  Goose 
and  Marietta  plums  are  much  less  affected  in  all  regions.  The 
native  cherries  are  more  resistant  than  such  as  the  Montmorency. 
The  fungus.  The  small  tufts  of  the  fungus,  commonly  called 
mold  tufts,  which  appear  on  affected  fruits  and  occasionally  on 
blighted  twigs  are  made  up  of  conidiophores  and  the  numerous 
conidia  to  which  they  give  rise.  The  production  of  the  aerial 
conidia  usually  indicates  that  the  substratum  is  considerably  pene- 
trated by  the  mycelium.  This  mycelium  is  light  brown  in  color, 
rather  closely  septate,  considerably  branched,  unequal  in  diameter, 
and  somewhat  nodulose  or  occasionally  cellular  in  appearance.  It 
is  often  vacuolate  and  may  contain  bodies  differentiated  as  resting 
mycelial  cells,  or  perhaps  properly  designated  chlamydospores. 


FUNGOUS  DISEASES  OF  PLANTS 


On  blighted  branches  of  the  peach  the  mycelium  has  been 
found  (Smith)  to  grow  most  abundantly  in  the  cambium  and  soft 
bast,  these  tissues  disappearing  in  large  measure  with  the  forma- 
tion of  extensive  gum  pockets  (Fig.  71). 

The  conidiophores  arise  as  short  hyphae,  which  soon  become 
septate  at  the  extremities,  branched  and  nodulose.  The  branching 
proceeds  in  an  indefinite  and  usually  irregular  or  semidichotomous 
fashion  (Fig.  72,  a  and  b).  From  the  apex  of  these  branches 
toward  the  base  conidia  are  rapidly  cut  off,  these  cells  remaining 
for  a  time  simply  moniliform  or  as  branched  chains,  each  con- 
striction between  the  nodulations  eventually  marking  the  line  of 


FlG.  72.     SCLE ROTINIA  FRUCTIGENA  .'    CONIDIOPHORES    AND    CONIDIA, 

SECTION  OF  APOTHECIUM,  Ascus,  AND  ASCOSPORES 

separation  between  adjacent  spores.  The  spores  germinate  readily, 
and  often  while  still  massed  in  the  tuft  of  conidiophores,  that  is, 
before  being  blown  or  brushed  away.  Germination  studies  have 
shown  that  many  of  the  conidia  may  live  through  until  the  suc- 
ceeding season,  and,  as  indicated,  the  mycelium  is  even  more 
capable  of  effective  hibernation. 

Ordinarily  no  apothecial  stage  has  been  observed  to  intervene 
regularly  in  the  life  cycle  of  this  fungus,  and  the  ascosporous  or 
Sclerotinia  stage  is  not  believed  to  be  important  to  continue  the 
propagation  of  the  fungus.  During  the  spring  of  1902  the  Scle- 
rotinia stage  was  found  (Norton)  quite  commonly  in  the  orchards 
of  Maryland.  The  apothecia  were  discovered  arising  from  scle- 
rotia,  which  might  be  developed  either  within  the  tissues  or  on 


ASCOMYCETES  193 

the  surface  of  the  mummied  fruits.  The  fruits  upon  which  this 
stage  appeared  had  been  lightly  covered  with  sandy  soil  for  at 
least  a  year.  In  1906  this  stage  was  extremely  common  through- 
out the  West.  Conditions  seemed  to  be  most  favorable  for  its  de- 
velopment where  the  fruit  had  lain  for  eighteen  months  in  little 
depressions  in  the  sod,  and  fairly  well  covered  by  grass  debris. 
The  stalk  or  stipe  of  the  apothecium  was  from  .5  to  3  cm.  in 
length,  depending  upon  the  distance  of  the  mummy  beneath  the 
soil.  The  stipe  is  dark  brown  and  the  slightly  bell-shaped  disk 
is  a  shade  lighter.  The  latter  is  usually  5-8  mm.  in  diameter, 
though  it  may  range  from  2  to  15  mm.  The  general  appearance 


FIG.  73.   APOTHECIA  OF  SCLEROTINIA  FROM  MUMMIED  PLUMS 

of  the  apothecia  is  shown  in  Fig.  73.  The  stipe  consists  of  a 
medulla  of  elongated,  intertwined,  brown  cells  and  a  cortex  of 
shorter,  darker  ones,  the  latter  being  continued  in  a  tissue  pro- 
jecting beyond  the  hymenium.  The  asci  are  cylindrical-clavate, 
125-215  x  7-10 /-i.1  They  arise  from  a  dense  layer  of  small 
hyphae,  differing  from  the  general  medullary  hyphae  merely  in  be- 
ing more  closely  intertwined  (Fig.  72,  c  and  d).  The  ascospores 
are  ellipsoidal  and  measure  10-15  x  5 -8 ft.  They  are  obliquely 
uniseriate,  or  subseriate.  The  paraphyses  are  characteristic  of 
many  Pezizaceae,  —  hyaline,  septate,  simple  or  branched,  filiform, 
and  slightly  swollen  at  the  tips. 

1  Reade,  J.  M.    Preliminary  Notes  on  Some  Species  of  Sclerotinia.    Annales 
Mycologici  6  :  109-116.    1908. 


194  FUNGOUS  DISEASES  OF  PLANTS 

Control.  Preventive  treatment  should  be  begun  in  late  winter 
or  very  early  spring  and  must  consider  two  possible  sources 
of  infection  :  (i)  conidia  adherent  to  bark  or  bud  scales,  and 
(2)  the  mummied,  diseased  fruits  or  blighted  twigs.  A  thorough 
spraying,  equivalent  to  disinfection  with  strong  Bordeaux  (6-6-50), 
would  be  effectual  against  the  free  conidia.  In  addition  to  such 
spraying,  however  (and  it  may  be  well  to  do  this  in  late  autumn), 
it  is  essential  to  destroy  the  old,  diseased  fruits.  Prune  them  or 
knock  them  from  their  attachment  to  the  twigs,  rake  them  from 
beneath  the  trees,  and  destroy  or  turn  under  deeply.  Spores  may 
be  blown  long  distances,  however,  so  that  an  appearance  of  the 
disease  may  be  expected  at  any  time  during  the  growing  season, 
aside  from  the  fact  that  it  is  hardly  possible  to  kill  all  adherent 
conidia.  In  some  sections  of  the  country  a  3-4-50  Bordeaux 
made  with  good  lime  has  been  used  advantageously  after  foliage 
and  fruit  are  well  developed,  with  no  injury  resulting  either  to 
peaches  or  Japanese  plums ;  but  this  is  not  uniformly  the  case, 
and  seasonal  conditions  unquestionably  have  a  considerable  in- 
fluence on  the  amount  of  injury  caused  by  the  spray.  It  might, 
where  practicable,  be  employed  until  the  fruits  are  more  than 
half  grown,  after  which  time  some  other  liquid  spray  or  Bordeaux 
dust  should  be  .substituted.  It  is  sometimes  advisable  to  use  a 
copper  acetate  solution  (6  ounces  to  50  gallons)  when  color  be- 
gins to  appear  in  the  fruit.  During  a  season  of  infrequent  rains 
the  writer  has  used  a  lime  spray  with  some  success. 

Some  experiments  have  recently  been  made l  with  the  lime- 
sulfur  spray,  and  it  is  sufficiently  promising  to  warrant  trial. 
Apparently,  the  safest  and  most  effective  preparation  is  made 
by  mixing  10  pounds  of  sulfur  and  15  pounds  of  good  lime. 
Upon  slaking  the  lime  the  sulfur  is  "self-cooked"  from  the 
heat  generated,  and  the  mixture  is  finally  diluted  to  50  gallons. 
During  a  single  fairly  dry  season  (a  most  favorable  one  for  this 
mixture)  the  loss  has  been  considerably  reduced,  —  73  per  cent 
in  the  unsprayed  plot  as  compared  with  from  10  to  30  per  cent 
in  the  sprayed. 

1  Faurot,  F.  W.  Brown  Rot  of  Peach.  Mo.  State  Hort.  Soc.  Kept.  (1907) : 
285-289.  (Scott,  who  cooperated  in  this  work,  has  also  published  the  results  of 
these  experiments  in  detail.  Compare  Bureau  Plant  Ind.,  U.  S.  Dept.  Agl.  Circular 
1  :  12-16.  1908.) 


ASCOMYCETES  195 

Sclerotinia  Vaccinii  (Wor.)  Rehm.1  This  species  occurs  on 
shoots,  leaves,  and  berries  of  the  cowberry,  Vaccinium  Vitis- 
idcea.  In  this  fungus  the  chains  of  conidia  show  characteristic 
"  disjunctors."  The  latter  are  fusiform  cellulose  structures  sepa- 
rating the  spores,  and  apparently  important  in  dissemination. 
The  conidial  surface  possesses  an  amygdaline  aroma,  by  which 
insects  are  supposedly  attracted.  The  diseased  berries  are  yell<5w- 
brown  when  ripe.  From  sclerotia  in  mummied  fruits  which  have 
lain  on  the  ground  over  winter  the  apothecia  are  developed.  The 
mature  ascospores  measure  14-17  X  7-9  p. 

Sclerotinia  Aucupariae  Ledw.2  has  been  found  in  Finland  and 
in  Germany  on  the  leaves  and  fruit  of  Pints  Aucuparia. 

Sclerotinia  baccarum  Schroet.3  is  the  cause  of  the  sclerotial 
disease  of  the  bilberry,  Vaccinium  Myrtillus.  In  this  species  the 
apothecia  are  relatively  large  and  stout,  measuring  5-10  mm.  in 
diameter,  with  stalks  often  5  cm.  in  length.  The  spores  are 
18-20  x  9/4. 

Sclerotinia  megalospora  Wor.,3  on  the  berries  and  leaves  of  the 
crowberry,  Empetrum  nigrum,  has  large,  more  nearly  spherical 
conidia  than  those  above  described,  and  the  ascospores,  invested 
with  a  distinct  gelatinous  envelope,  measure  20-25  x  14-16/4. 

Sclerotinia  Oxycocci  Wor.3  produces  the  sclerotial  disease  of  the 
cranberry,  Vaccinium  Oxycoccus.  This  species  is  morphologically 
and  physiologically  interesting  on  account  of  the  difference  in 
size  of  the  spores,  four  being  large  and  capable  of  germination, 
while  the  other  four  are  considered  to  be  ill  developed  and  in- 
capable of  germination.  This  suggests  an  interesting  differentia- 
tion of  the  nuclei.  Even  the  larger  spores  are  relatively  small  for 
this  group,  measuring  12-14  X  6-7/4. 

Sclerotinia  heteroica  Wor.  &  Nawasch.4  According  to  Woronin 
this  species  produces  upon  Vaccinium  uliginosum  a  conidial  stage, 
which  conidia  are  able  successfully  to  infest  the  ovaries  of  Ledum 
palustre,  but  no  conidia  are  produced  on  Ledum.  On  the  latter 
host,  however,  the  sclerotial  stage  is  developed.  This  fungus 

1  Woronin.  Ueber  die  Sclerotienkrankheiten  d.  Vaccinieen-Beeren,  /.  c. 

2  Woronin.    Ber.  d.  deut.  hot.  Ges.  9  :   102-103. 

3  Woronin.    Ueber  die  Sclerotienkrankheiten  d.  Vaccinieen-Beeren,  /.  c, 
*Nawaschin.    Ber.  d.  deut.  bot.  Ges.  12  :  117-119. 


196  FUNGOUS  DISEASES  OF  PLANTS 

apparently  requires  two  hosts  to  complete  its  development  and  is, 
therefore,  an  instance  of  what  is  denoted  heteroecism,  a  condition 
discussed  more  at  length  under  the  rust  fungi. 

Sclerotinia  Rhododendri  Fischer,1  like  the  preceding,  appears 
to  be  hetercecious  in  character.  It  is  found  on  Rhododendron 
ferrugineum  and  Rhododendron  hirsutum. 

VIII.    GRAY  MOLD,  OR  BOTRYTIS  DISEASE 
Sclerotinia  Fuckeliana  De  Bary 

BROOKS,  F.  T.    Observations  on  the  Biology  of  Botrytis  cinerea.    Ann.  Bot. 

22:  479-484.  ffigs.  1-4.     1908. 
ISTVANFFI,  G.  DE.  Etudes  microbiologiques  et  mycologiques  sur  le  rot  gris  de 

la  vigne.   Ann.  d.  1'institut  central  ampel.  roy.  Hongrois(i9O5):    183-360. 
KISSLING,  E.    Zur   Biologic    der    Botrytis  cinerea.     Hedwigia  28 :   227-256. 

1889. 
NORDHAUSEN,  M.    Beitragc  zur  Biologic  parasitaren    Pilze.    Jahrb.  f.  wiss. 

Bot.  33:    1-46.    1898. 
SMITH,  R.  E.    Botrytis  and  Sclerotinia.    Botan.  Gaz.  29 :  369-407.  pis.  25- 

27.  figs.  1-3.    1900. 
SMITH,  R.  E.    The  Parasitism  of  Botrytis  cinerea.    Botan.  Gaz.  38:  421-436. 

1902. 

Occurrence  and  effects.  In  the  conidial  stage  this  is  one  of  the 
most  common  fungi  known  upon  vegetation.  It  may  propagate 
itself  indefinitely  as  a  saprophyte  upon  fallen  or  dejected  flowers 
and  leaves,  or  upon  decaying  organic  matter.  Again,  it  may,  as 
a  parasite,  produce  a  variety  of  rots,  decays,  or  stem  diseases, 
especially  in  greenhouse  or  other  plants  grown  under  moist, 
warm  conditions. 

In  Europe  it  is  important  as  a  disease  of  the  leaves  and  fruit 
of  the  grape.  While  such  injuries  may  be  serious,  the  abundance 
of  this  fungus  on  the  fruit,  in  certain  regions,  late  in  the  season 
gives  promise  'of  high-class  wine  production.  The  grapes  are  then 
juicy  and  rich  in  sugar.  It  attacks  other  woody  plants.  Smith  re- 
gards the  Botrytis  Douglasii  Tubeuf,2  reported  destructive  to 
young  conifers,  as  synonymous  with  this  species,  and  he  has 
found  it  responsible  for  a  disease  of  the  linden  ( Tilia  parviflord) 
in  the  nursery.  It  seems  to  be  the  less  frequent  cause  of  lettuce 
"  drop  "  in  the  greenhouse.  This  disease,  subsequently  discussed 

1  Fischer.   Ber.  d.  schweiz.  hot.  Ges.    1894. 

2  Tubeuf,  K.  von,    Botan.  Centrbl.  33  :  347..    1888, 


ASCOMYCETES 


197 


more  at  length,  may  begin  and  develop  in  various  ways  when 
Botrytis  is  the  cause,  but  it  is  finally  known  by  the  complete 
collapse  of  the  lettuce  heads  due  to  the  death  of  the  stem  and  leaf 
bases.  The  conidial  stage  is  also  associated  with  various  damping-off 
diseases,  and  it  is  believed  by  Smith  to  be  the  organism  studied  by 
Marshall  Ward  as  the  cause  of  an  important  lily  disease.1  In  all 
cases  the  conidial  stage  of  the  fungus  may  develop  abundantly 
upon  the  dead  parts,  and  it  has  the  appearance  of  a  gray  mold. 


FIG.  74.    BOTRYTIS  CINEREA.    (After  R.  E.  Smith) 
a,  portion  of  conidiophore  ;  ^,  organ  of  attachment 

The  fungus :  morphology  and  biology.  Under  Sclerotinia 
Fuckeliana  it  is  intended  to  include  the  forms  of  disease  which 
may  be  attributed  in  Europe  to  Botrytis  cinerea  Pers.  and  in 
America  to  Botrytis  vulgaris  Fr.  It  has  been  satisfactorily  dem- 
onstrated that  these  two  names  apply  to  a  single  species,  a  typical 
conidiophore  of  which  is  illustrated  in  Fig.  74.  The  observations 
of  De  Bary  first  connected  this  conidial  stage  with  an  apothecial 
form,  Sclerotinia  Fuckeliana,  produced  from  sclerotia  of  the  Bo- 
trytis on  grape.  Subsequently  doubt  arose  regarding  this  connec- 
tion, since  many  observers  failed  repeatedly  to  secure  under  any 

1  Ward,  H.  Marshall.    Ann.  Bot.  2  :  319-382.  ph.  20-24.     l888- 


I98 


FUNGOUS  DISEASES  OF  PLANTS 


conditions  the  perfect  form  from  sclerotia  of  the  Botrytis.  It  would 
seem  that  Istvanffi  has  now  secured  substantial  proof  that  these 
are  pleomorphic  stages  of  a  single  fungus. 

Much  interesting  biological  work  has  been  done  upon  this 
fungus.  Infection  results  most  readily  from  sclerotia  or  from 
a  mycelium  which  has  been  growing  saprophytically.  Infection 
frequently  fails  when  conidia  germinate  directly  upon  the  sur- 
faces of  delicate  parts.  Upon  penetrating  a  plant  there  is,  first, 
a  direct  poisoning  effect,  supposedly  due  to  oxalic  acid,  resulting 
in  the  death  of  adjacent  cells ;  and,  second,  there  is  more  or  less 
digestion  of  the  cell  contents  and  membranes. 


FIG.  75.    SCLEROTINIA  LiBERTiANA.    (After  R.  E.  Smith) 
a,  sclerotia  and  apothecium  ;  £,  penetration  of  hyphae 

Control.  In  the  case  of  this  fungus,  as  well  as  the  species  of 
Sclerotinia  next  discussed,  good  sanitation  is  important.  Never- 
theless, in  the  greenhouse  it  may  be  necessary  to  sterilize  the 
soil  in  order  to  control  the  disease  effectively  when  it  becomes 

virulent. 

IX.    LETTUCE  DROP 

Sclerotinia  Libertiana  Fuckel 

HUMPHREY,  J.  E.  Diseases  of  the  Cucumber  Plant.  A  Sclerotium  Disease. 
Mass.  Agl.  Exp.  Sta.  Kept.  10:  212-224.  pis.  1-2.  1892. 

SMITH,  R.  E.  Botrytis  and  Sclerotinia :  Their  Relation  to  Certain  Plant  Dis- 
eases and  to  Each  Other.  Bot.  Gaz.  29 :  369-407.  pis.  25-27. 

STONE,  G.  E.,  and  SMITH,  R.  E.  "  Drop  "  of  Lettuce.  Mass.  (Hatch)  Exp. 
Sta.  Rept.  9:  79-81.  1897.  (Compare,  also,  10:  55-58,  1898;  and  11: 
149-151,  1899.) 


ASCOMYCETES  199 

Symptoms,  effects,  and  hosts.  It  is  difficult  to  determine  how 
many  of  the  reported  sclerotial  diseases  of  greenhouse  and  garden 
crops  may  be  due  to  this  fungus.  It  is  unquestionably,  however, 
one  of  the  most  disastrous  of  the  sclerotium-producing  fungi,  and 
it  is,  moreover,  widely  distributed  and  not  readily  controlled.  So 
far  as  can  be  judged  from  the  studies  and  experiments  which 
have  been  made,  it  is  the  cause  of  the  worst  type  of  the  lettuce 
"drop,"  a  disease  of  great  importance  in  the  greenhouses  of  the 
eastern  states. 

As  this  disease  commonly  occurs  there  is  little  or  no  evidence 
of  the  incipient  stages  in  the  form  of  definite  spots  or  ulcers. 
The  host  plants  may  show  some  evidences  of  flagging,  in  a  short 
time  there  are  indications  of  water-soaked  areas  over  the  stem 
and  basal  portions  of  leaves,  and  finally  the  whole  plant  collapses 
and  melts  into  a  formless  mass. 

Even  from  early  evidences  of  the  disease  fungus  threads  may 
appear  upon  the  surface  of  the  leaf,  and  this  mycelium  may  be- 
come superficially  conspicuous,  even  resulting  in  the  development 
of  small  sclerotia.  These  appear  first  as  white  specks  and  later 
take  the  form  of  deep  black,  rather  irregular  sclerotia,  as  shown 
in  Fig.  75,  a.  This  fungus  quickly  spreads  from  plant  to  plant 
through  the  soil,  and  furthermore,  in  its  relation  to  healthy 
plants,  results  almost  invariably  in  the  production  of  the  disease. 
De  Bary  showed  that  ascospores  are  commonly  ineffective  in  pro- 
ducing direct  infection,  but  sclerotia  or  bits  of  the  mycelium  may 
serve  for  inoculation  purposes.  The  Sclerotinia  Libertiana  type 
of  sclerotium  will  yield  almost  invariably  the  apothecia  of  the 
Sclerotinia. 

This  fungus  is  apparently  widespread.  It  has  been  reported  by 
various  observers  as  a  cause  of  destructive  diseases  of  hemp,  rape, 
cucumbers,  and  of  many  forced  vegetables  and  bulbous  plants.  A 
disease  of  the  tobacco,  discussed  by  Clinton,1  has  also  been  attrib- 
uted to  this  fungus. 

The  life  cycle.  In  no  case  has  it  been  possible  positively  to  iden- 
tify a  conidial  stage  in  the  life  cycle  of  this  species,  although  Botrytis 
cinerea  has  frequently  been  found  upon  plants  unquestionably 

1  Clinton,  G.  P.  Tobacco  Diseases.  Stem  Rot.  Conn.  Agl.  Exp.  Sta.  Rept. 
(10,06)  :  326-329.  pis.  20  a,  b  ;  21  a. 


200  FUNGOUS  DISEASES  OF  PLANTS 

affected  with  this  sclerotial  disease.  From  a  series  of  experi- 
ments extending  through  several  years,  Smith  was  unable  by 
any  means  to  produce  a  conidial  stage  from  cultures  of  the 
Sclerotinia  Libertiana  sclerotia,  and  he  believes,  moreover,  that 
there  exists  another  type  of  this  fungus  in  which  no  conidia  are 
produced  and  in  which  the  more  minute  sclerotia  are  incapable 
of  producing  the  apothecia.  Whether  or  not  there  is  any  connec- 
tion between  the  large  sclerotinial  type,  which  must  be  designated 
as  Sclerotinia  Libertiana,  and  the  smaller  type  above  referred  to, 
it  is  unquestionably  true  that  there  exists  a  disease  of  lettuce  and 
other  greenhouse  plants  of  which  the  small  sclerotium-producing 


FIG.  76.   THE  LETTUCE  DROP:  CONTROL  (HEALTHY)  AND  INOCULATED 
(DISEASED)  PLANTS 

fungus  is  the  cause.  The  writer  has  found  this  type  of  the  fungus 
to  be  the  cause  of  an  important  disease  of  lettuce  in  New  York 
and  Boston,  and  inoculation  experiments  have  invariably  shown 
the  disease  to  be  unusually  virulent  (Fig.  76).  Sclerotinia  Liber- 
tiana has  been  several  times  reported  as  an  important  disease  of 
the  cucumber,  and  according  to  Humphrey  it  is  rather  common 
in  the  cucumber  houses  in  Massachusetts.  Humphrey  supposed, 
however,  that  the  Botrytis  which  he  found  upon  diseased  plants 
was  connected  with  the  sclerotial  stage,  but  no  sufficient  proof  of 
such  connection  is  afforded  by  the  work  which  he  reports. 

The  sclerotia  of  this  species  are  said  to  reach  3  cm.  in  length 
in  exceptional  cases.  The  asci  are  cylindrical,  and  measure  130- 
135  X  8-io/Uj  while  the  spores  are  small,  —  9-13  X  4-6.5  p. 


ASCOMYCETES  2OI 

X.    STEM  ROT  OF  CLOVER 

Sclerotinia  Trifoliorum  Eriks. 

CHESTER,  F.  D.    Rot  of  the  Scarlet  Clover.    Del.  Agl.  Exp.  Sta.  Rept.  3 : 

84-88.    1890. 
ERIKSSON,  J.    Bot.  Centrbl.  1 :  296. 

This  fungus  is  occasionally  very  destructive  to  various  species 
of  clover  (Trifolium)  in  Europe,  and  it  has  several  times  been 
reported  as  epidemic  in  the  United  States.  In  this  country,  how- 
ever, it  is  not  so  widely  distributed  or  so  constant  in  its  injurious 
effects  as  to  have  been  often  observed.  The  effect  of  this  fungus 
upon  the  host  is  to  produce  a  decay  near  the  base  of  the  stool,  or 
practically  at  the  surface  of  the  ground,  as  the  result  of  which  the 
plant  wilts.  The  mycelium,  which  is  from  the  beginning  evident 
on  the  surface,  invades  the  tissues  and  ordinarily  by  the  time  that 
the  plant  is  killed  numerous  small,  black  sclerotia  are  produced 
upon  the  surface  of  the  affected  parts.  The  sclerotia  vary  in  size 
from  i  to  5  or  6  mm.  in  diameter.  Sown  upon  moist  sand  or 
wintered  upon  the  decaying  remains  of  the  host  there  are  pro- 
duced the  following  spring  the  brown  apothecia  characteristic  of 
this  species.  The  asci  are  long  cylindrical,  about  180  X  12  JJL. 
Ascospores,  which  are  disseminated  in  the  early  spring,  lose 
their  power  of  germination  upon  being  dried,  and  it  would  seem, 
therefore,  that  they  must  penetrate  the  host  at  this  time.  It  is 
claimed,  on  the  other  hand,  that  the  sclerotia  may  retain  their 
vitality  for  a  period  of  several  years  if  the  conditions  are  un- 
favorable for  germination.  Some  regard  this  fungus  as  identical 
with  Sclerotinia  Libertiana. 

Sclerotinia  Betulae  Wor.1  This  birch  catkin  disease  is  common 
in  birch  forests  of  Russia.  Sclerotia,  so  far  as  is  known,  are  pro- 
duced during  the  development  of  the  catkins,  falling  and  remain- 
ing on  the  ground  over  winter.  The  apothecia  are  formed  the 
following  spring,  each  sclerotium  producing  several  small  apo- 
thecia of  light  color.  The  fungus  has  also  been  found  in  Europe, 
Asia,  and  America. 

Sclerotinia  tuberosa  (Hedw.)  Fckl.  develops  enormous  sclerotia 
on  the  rhizomes  of  Anemone  nemorosa. 

1  Tubeuf.   Diseases  of  Plants,  /.  c.,  261. 


202  FUNGOUS  DISEASES  OF  PLANTS 

XI.    LARCH  CANKER 
Dasyscypha  WiUkommii  Hartig. 

HARTIG,  R.    Die  Larchenkrankheiten,   insbesondere   der   Larchenkrebspilz. 
Untersuch.  aus  d.  Forstbotan.  Institut  Miinchen  1  :  63-87.    1880. 

Occurrence  and  effects.  The  larch  canker  is  one  of  the  most 
important  diseases  of  this  host  in  certain  districts  of  Europe.  It 
is  particularly  abundant  in  the  moist,  marshy,  mountain  meadows, 
but  is  seldom  of  importance  on  hillsides  or  slopes.  The  fungus 
is  a  typical  canker-producing  organism,  and,  so  far  as  is  known,  it 
gains  entrance  to  the  host  only  through  wounds.  It  spreads  most 
rapidly  in  the  phloem  elements  and  rapidly  causes  the  death  of 
the  bark.  The  diseased  areas  become  shrunken  and  brown.  The 
bark  may  peel  away  in  places  and  pronounced  cankers  develop. 
The  fungus  appears  to  spread  rapidly  only  during  seasons  when 
the  host  plant  is  comparatively  inactive,  as  during  the  autumn 
and  winter.  The  wounds  of  the  previous  year  may,  therefore, 
be  practically  healed  over  during  the  growing  season,  but  the 
following  autumn  the  fungus  continues  its  spread,  and  in  time 
large  limbs  or  trunks  may  be  completely  girdled  and  death  result. 
The  needles  on  affected  twigs  begin  to  show  the  presence  of  the 
fungus  during  the  late  summer. 

The  fungus.  Upon  the  death  of  the  bark  the  fungus  appears 
superficially  in  the  form  of  creamy  or  yellowish-white  stromatic 
tufts.  Upon  the  minute  conidiophores  there  are  produced  simple 
hyaline  conidia.  The  latter  have  not  been  germinated  and  do  not 
appear  to  be  important  in  the  immediate  distribution  of  the  fungus. 
Later  in  the  season  the  apothecia  may  appear  on  the  diseased  areas 
if  there  is  sufficient  moisture.  The  apothecia  are  short  stalked, 
almost  sessile,  yellowish  without,  and  orange  colored  within.  The 
asci  measure  about  1 20  x  9  //-.  They  are  cylindrical  in  form  and 
contain  invariably  eight  ovoidal,  unicellular  spores.  Between  the 
asci  are  interspersed  a  considerable  number  of  filiform  paraphyses. 
Inoculation  experiments  have  demonstrated  that  this  fungus  is  the 
cause  of  the  canker  with  which  it  is  associated.  No  preventive 
measures  can  be  recommended  when  the  fungus  is  once  estab- 
lished on  larch  plantations,  and,  therefore,  in  locating  new  planta- 
tions, one  should  bear  in  mind  the  conditions  under  which  the 
fungus  is  most  disastrous. 


ASCOMYCETES  203 

XII.  MOLLISIACE/E 

This  family  differs  from  the  Helotiaceae  largely  in  texture,  the 
former  being  tougher,  and  as  a  rule  made  up  of  hyphal  cells 
modified  in  a  prosenchymatic  or  fibrous  manner.  The  spores  are 
hyaline  and  very  similar  to  those  of  the  Helotiaceae.  The  only 
genus  of  importance  in  producing  plant  diseases  is  Pseudopeziza. 


FIG.  77  a.   ALFALFA  LEAF  SPOT.    (Photograph  by  H.  H.  Whetzel) 

Pseudopeziza.  In  this  genus  the  apothecium  is  formed  beneath 
the  epidermis,  which  is  later  ruptured,  and  the  mature  fruit  body 
is  relatively  simple  in  structure  and  shallow.  The  asci  contain  eight 
unicellular  spores. 

XIII.    ALFALFA  LEAF  SPOT 
Pseudopeziza  Medicaginis  (Lib.)  Sacc. 

COMBS,  ROBT.    The  Alfalfa  Leaf  Spot  Disease.   Iowa  Agl.  Exp.  Sta.  Built. 
36:  858-859. 

The  alfalfa  leaf  spot  is  often  very  abundant  both  in  Europe 
and  America,  and  particularly  injurious  during  rather  dry  seasons. 


204 


FUNGOUS  DISEASES  OF  PLANTS 


FIG.  77  b.  ALFALFA  DEFOLIATED  BY 
THE  LEAF  SPOT  FUNGUS.    (Photo- 
graph by  H.  H.  Whetzel) 


Small  sooty  brown  or  black  spots 
about  -jL-  inch  in  diameter  are 
produced,  first  evident  on  the 
upper  surfaces  of  the  leaves  (Fig. 
78).  In  these  spots  there  appear 
later  in  the  season  the  relatively 
simple,  sessile  apothecia,  which 
are  formed  beneath  the  epidermis 
and  break  through  at  maturity. 
The  spots  are  often  very  numer- 
ous, causing  defoliation  of  many 
of  the  leaves  by  the  latter  part 
of  summer.  These  structures  are 
saucer-shaped,  flat,  and  light  in 
color,  at  first  fleshy  in  texture. 
The  club-shaped  asci  bear  eight 
unicellular  colorless  spores  in 
two  series,  measuring  1 0-14/4  in 
length.  Paraphyses  are  also  pres- 
ent. The  mycelium  is  very  local 
and  confined  to  the  area  of  the 
spots.  This  fungus  is  very  closely 
related  to  the  species  causing  a 
leaf  spot  of  clover,  Pseudopesiza 
Trifolii,  and  with  this  species  it 
may  be  identical.  No  practical 
method  of  controlling  this  dis- 
ease has  been  developed. 


XIV.   ANTHRACNOSE  OF  CURRANTS 
Pseudopeziza  Ribis  Kleb. 

DUDLEY,  W.  R.    Anthracnose  of  Currants.    Cornell  Agl.  Exp.  Sta.  Built.  15 : 

196-198.    1889. 
KLEBAHN,  H.    Untersuchungen  iiber  einige  Fungi  imperfect!  und  die  zuge- 

horigen  Ascomycetemforem.    Ill  Gloeosporium  Ribis  (Lib.)  Mont,  and 

Desm.  Zeitsch.  f.  Pflanzenkr.  16:  65-83.  pis.  3-4.    1906. 
STEWART,  F.  C.    An  Epidemic  of  Currant  Anthracnose.    N.  Y.  (Geneva)  Agl. 

Exp.  Sta.  Built.  199  :  64-80.    1 90 1 . 


ASCOMYCETES 


205 


Distribution  and  occurrence.  This  anthracnose  is  a  disease  well 
known  in  Europe  and  America.  Periodically  since  1884  it  has  been 
mentioned  as  a  destructive  fungus  to  both  white  and  red  currants 
in  New  York.  The  fungus 
has  also  been  found  upon 
black  currants  and  goose- 
berries, but  it  has  never, 
apparently,  amounted  to  an 
epidemic.  Among  red  cur- 
rants Stewart  observed  that 
Prince  Albert  and  President 
Wilder  were  practically  free 
from  injury  where  Fay's 
Prolific  and  Victoria  were 
seriously  affected. 

Affected  leaves  are  more 
or  less  covered  with  small 
brown  spots,  as  shown  in 
Fig.  1  58.  When  the  trouble 
is  serious  the  leaves  turn 

yellow  and  drop.     The  fun- 

i  ,.  , 

gus  also  occurs  on  petioles, 

young  canes,  fruit  stalks,  and  fruits.    It  is  believed  that  it  may 
pass  the  winter  on  the  canes. 

The  fungus.  Until  1906  this  fungus  was  known  by  an  im- 
perfect stage  alone,  which  like  that  of  the  bitter  rot  of  the  apple 
subsequently  discussed  was  referred  to  the  genus  Glceosporium, 
and  bore  the  name  Gloeosporium  Ribis.  The  Gloeosporial  stage 
(cf  .  Gloeosporium)  is  in  fact  the  only  stage  of  the  fungus  which  is 
produced  upon  the  growing  plant.  The  pustules  or  acervuli  con- 
sist of  a  stromatic  portion  from  which  arise  numerous  conidiophores, 
bearing  elliptical  or  strongly  curved,  falcate  conidia.  These  fruit- 
ing masses  rupture  the  epidermis  and  the  spores  escape  in  a  gelat- 
inous mass.  The  acervuli  are  produced  very  abundantly  on  both 
surfaces  of  the  leaves  but  particularly  upon  the  upper  surfaces. 
The  spores  are  commonly  19  x  7/*,  varying,  however,  from  12- 
24  x  5-9  IJL.  Formerly,  it  was  suggested  that  this  gloeosporial  form 
might  be  connected  with  Gnomoniella  circinata  (Fckl.)  Sacc, 


FlG-    7^-     PSKUDOPEZIZA    MEDICAGINIS: 
STRUCTURAL  FEATURES.    (After  Comes) 


206  FUNGOUS  DISEASES  OF  PLANTS 

Klebahn  in  his  investigations  of  this  fungus  ascertained  that 
when  the  leaves  are  wintered  over  under  suitable  conditions  of 
moisture  an  ascigerous  stage  is  developed  the  following  spring. 
This  stage  proved  to  be  a  Pseudopeziza ;  that  is  to  say,  a 
Tseudopeziza  was  one  of  the  most  abundant  of  the  perithecial 
stages  found  on  wintered  leaves.  The  spores  of  other  perithecial 
forms  yielded  upon  inoculation  of  the  growing  leaves  no  result, 
whereas  spores  of  the  Pseudopeziza  developed  in  due  course  of 


FIG.  79.   ANTHRACNOSE  ON  CURRANT  LEAF.  (Photograph  by 
F.  C.  Stewart) 

time  the  Glceosporial  stage  upon  growing  parts.  The  ascigerous 
stage  develops  as  a  small  fungous  body  of  rapidly  growing  tissue, 
completely  immersed  in  the  leaf,  and  more  or  less  surrounded  by 
the  old  hyphae  of  the  Glceosporial  form.  With  further  develop- 
ment the  epidermis  is  ruptured  and  the  apothecium  opens  as  a 
fleshy  disk-shaped  structure,  the  basal  portions  of  which  consist 
of  more  or  less  pseudoparenchymatous  tissue  from  which  arise 
numerous  asci'  and  paraphyses.  The  basal  portion  remains  in 
part  surrounded  by  thick-walled  cells  of  the  old  mycelium,  as 


ASCOMYCETES 


207 


shown  in  Fig,  80,  b.  The  asci  are  club-shaped  and  bear  eight 
hyaline  ovoidal  spores.  The  paraphyses  are  simple  or  branched, 
sometimes  once-septate  and  slightly  club-shaped. 

This  fungus  shows  in  pure  culture  certain  growth  characteristics 
which  seem  to  differentiate  it  somewhat  sharply  from  other  species 
of  Gloeosporium.  In  the  first  place  it  grows  slowly  upon  nutrient 
agar,  several  months  being  required  to  produce  a  colony  of  several 
millimeters  in  extent.  The  hyphae  become  considerably  colored 


FIG.  80.   PSEUDOPEZIZA  RIB  is.    (b,  after  Klebahn) 
a,  conidial  stage  ;  6,  section  of  apothecium 

and  often  gray-green  in  appearance.  The  central  portion  of  the 
colony  gradually  forms  a  stromatic  body.  The  cultures  of  the 
ascus  stage  yielded  the  same  type  of  colony,  which  is  further 
proof  of  the  genetic  connection  between  the  two  spore  stages. 
This  is  the  first  time  that  a  fungus  with  all  the  characteristics 
of  a  Gloeosporium  has  been  experimentally  connected  with  an 
ascigerous  form  belonging  to  the  Discomycetes. 

XV.  PHACIDIACE^E 

In  this  family  the  apothecium  develops  with  a  surrounding 
stroma,   which    is   ordinarily  coherent   with    the    substratum.    At 


208 


FUNGOUS  DISEASES  OF  PLANTS 


the  outset  the  apothecium  is  closed,  but  opens  by  a  circular  or 
transverse  split,  and  the  edges  are  often  torn  or  bent  back  as 
distinct  lips  or  lobes.  The  apothecia  are  usually  tough  and 
leathery.  The  asci  and  paraphyses  form  a  very  closely  adherent 
layer,  in  which  the  paraphyses  overlap  above  the  summit  of 
the  asci,  forming  a  rather  definite  epithecium.  Rhytisma  is  the 
only  genus  which  is  here  of  importance. 


XVI.    THE  BLACK  SPOT  OF  MAPLE 
Rhytisma  Acerinum  (Pers.)  Fr. 

KLEBAHN,  H.  Bemerkungen  iiber  Rhytisma  acerinum  und  iiber  die  Arbeit 
des  Herrn.  Dr.  Julius  Miiller  iiber  die  Runzelschorfe.  Bot.  Centrbl.  58  : 
321-323.  1894. 

MULLER,  J.  Zur  Kenntniss  des  Runzelschorfes  und  der  ihm  ahnlichen  Pilze 
Jahrb.  f.  wiss.  Botanik  25:  607-627.  pis.  27-29.  1893. 

The  black  spot  of  the  maple  (Acer  spp.)  is  a  fungus  of  very 
wide  distribution,  but  the  amount  of  injury  caused  is  so  slight 
that  it  cannot  be  considered  of  much  economic  importance.  The 

affected  areas  of  the  leaf  are  so 
conspicuous,  however,  as  to  attract 
the  attention  of  all'  interested  in 
parasitic  fungi  (Fig.  81).  The 
fungus  occurs  upon  a  number  of 
species  of  Acer,  the  first  evidences 
of  the  spot  being  manifest  by  yel- 
low, thickened  areas  soon  after  the 
leaves  have  attained  full  size.  A 
cross  section  shows  that  beneath 

the  cuticle  there  are  produced  in 
^^  quantity  Qn  short  conidi(> 

phores  arising  from  a  stromatic  tissue  unicellular,  curved  conidia, 
and  these  conidia  serve  to  spread  the  fungus,  it  is  believed,  during 
the  same  season.  This  stage  is  referred  to  the  form  genus  Melas- 
mia.  The  tough  blackened  structures,  which  appear  in  the  affected 
spots  as  the  season  advances,  consist  in  reality  of  sclerotioidal 
masses  of  fungous  tissue,  black  without  but  white  within,  penetrat- 
ing all  medullary  parts  of  the  leaf.  These  areas  are  much  thicker 
than  the  normal  leaf.  After  the  fall  of  the  leaf  further  growth  or 


Fio.8..  THE  BLACK  SPOT  OF  MAPLE 


ASCOMYCETES 


209 


differentiation  takes  place  in  the  sclerotial  areas,  so  that  there  is 
finally  developed  by  the  next  spring  rather  unlimited,  complex 
apothecia,  often  1.5  cm.  broad,  which  rupture  by  irregular  fissures 
along  the  ridges  of  the  wrinkled  surface.  The  asci  are  club-shaped, 
and  bear  eight  needle-shaped  spores.  Numerous  paraphyses  with 
incurved  or  hooked  tips  are  present.  The  asci  are  120-130  x  9- 
lOyu-.  At  maturity  the  large  spores  (65-80  x  1.5-3^)  are  ejected 
forcibly  from  the  ascus,  doubtless  distributed  by  the  wind,  and 
they  are  provided  with  a  mucilaginous  membrane  which,  accord- 
ing to  Klebahn,  serves  for  adherence  to  the  host.  Artificial  infec- 
tion with  ascospores  has  been  effected,  and  after  such  infection 
the  pycnidial  stage  may  be  produced  within  about  eight  weeks. 

Among  other  common  and  conspicuous  species  of  Rhytisma 
of  wide  distribution  are  Rhytisma  Salicinum  (Pers.)  Fr.  occur- 
ring on  various  species  of  Salix ;  Rhytisma  Vaccinii  (Schw.)  Fr. 
on  species  of  Ericaceae,  notably  Vaccinium  arboreum  in  the 
Appalachians. 

XVII.  PERISPORIALES 

This  order  includes  a  few  families  well  distinguished  from  the 
preceding  Ascomycetes  by  the  presence  of  a  more  or  less  mem- 
branous, generally  spherical,  closed  fruit  body,  or  perithecium, 
produced  directly  on  the  mycelium.  In  the  two  families  which  may 
here  be  considered,  Perisporiaceae  and  Erysiphaceae,  there  is  no 
mouth  or  ostiolum.  The  families  may  be  distinguished  as  follows  : 

Perisporiaceae.  Mycelium  generally  dark  in  color ;  perithecium 
without  differentiated  appendages,  and  conidial  stages  not  com- 
parable to  the  form  genus  Oidium. 

Erysiphaceae.  Mycelium  generally  hyaline ;  perithecium  with 
appendages,  often  highly  modified ;  and  conidial  stage,  when 
present,  invariably  an  Oidium. 

XVIII.  PERISPORIACE^:1 

This  is  a  small  family  although  some  authors  may  include 
in  it  as  many  as  twenty  genera.  The  genera,  as  a  rule,  comprise 

1  The  two  genera  which  are  here  discussed  have  been  included  by  Fischer 
(Engler  and  Prantl,  /.  c.)  in  the  Plectascineae,  and  there  is  considerable  diversity 
of  opinion  as  to  their  true  position. 


210  FUNGOUS  DISEASES  OF  PLANTS 

very  few  species.  Some  are  parasitic  and  some  saprophytic, 
some  with  superficial  mycelium,  and  others  with  mycelium  pene- 
trating the  substratum.  Two  genera  which  are  important  in  this 
connection  are  Thielavia  and  Meliola.  In  the  former  genus  the 
Mycelium  is  immersed  in  the  host.  The  perithecia  are  mem- 
branous, without  appendages,  and  subsidiary  fruit  forms  include  a 
stage  with  endogenous  spores.  In  the  genus  Meliola,  the  mycelium 
is  superficial  and  brown.  The  perithecia  are  beset  with  simple  01 
branched  appendages.  The  spores  are  brown  and  two-celled. 

XIX.    ROOT  ROT  OF  TOBACCO,  VIOLETS,  PEAS,  LUPINES,  ETC 
Thielavia  basicola  (B.  &  Br.)  Zopf. 

BRIGGS,  L.  J.    The  Field  Treatment  of  Tobacco  Root-Rot.    Bur.  Plant  Ind., 

U.  S.  Dept.  Agl.  Circular  7:    1-8.    1908. 
CLINTON,  G.  P.    Root  Rot  of  Tobacco.    Conn.  Agl.  Exp.  Sta.  Rept  (1906): 

342-368.  pis.  29-32. 
THAXTER,  ROLAND.    Fungus  in  Violet  Roots.    Conn.  Agl.  Exp.  Sta.  Rept. 

(1891):   166-167. 
ZOPF,  W.    Ueber  die  Wurzelbraune  der   Lupinen,  eine  neue  Pilzkrankheit. 

Zeitsch.  f.  Pflanzenkr.  1:   72-76.  figs.  1,2.    1891. 

This  fungus,  which  is  now  known  to  cause  in  the  United 
States,  under  certain  climatic  and  soil  conditions,  a  serious 
disease  of  tobacco  (Nicotiana  Tabacum],  was  first  studied  in 
Europe  as  a  parasite  of  less  consequence  upon  peas,  lupines,  etc. 
The  morphology  of  the  fungus  and  its  relation  to  a  disease  of 
Senecio  elegans  was  established  in  1876.  The  fungus  was  found 
in  the  United  States  on  violets  (Viola  odoratd}  in  1891,  and  sub- 
sequently on  other  plants ;  but  in  1 906  it  was  recognized  in 
Connecticut  as  an  important  tobacco  parasite. 

Distribution.  Upon  one  or  more  of  its  hosts  the  fungus  has 
been  .found,  in  general,  from  Ohio  eastward  in  the  United  States, 
and  in  western  Europe  from  England  to  Italy.  The  fungus  has 
not  been  reported  from  the  southern  states  growing  tobacco, 
or  from  tropical  regions.  It  is  believed  that  abundant  moisture 
is  essential  for  serious  trouble  by  this  fungus,  lack  of  drainage 
and  other  factors  assisting  in  producing  this  condition.  Briggs 
has  recently  shown  that  the  presence  of  this  fungus  in  tobacco 
soils  is  an  indication  of  alkalinity,  a  condition  often  brought 
about  by  the  system  of  fertilization. 


ASCOMYCETES 


21 1 


Host  Plants.  The  following  is  a  list  of  the  natural  hosts,  as 
compiled  by  Clinton:  Ginseng,  Aralia  quinqnefolia ;  Begonia 
nibra  ;  Begonia  sp. ;  horse  radish,  Cockle  aria  Armoracia  ;  Cycla- 
men sp. ;  lupines,  Lupinus  albus,  Lupinus  angustifolius ,  Lupinus 
lutens,  and  Lupinus  thermis ;  Nemophila  auriculata ;  tobacco, 
Nicotiana  Tabacum ;  Onobrychis  Cristagalli ;  pea,  Pisum  sa- 
tivinn ;  Trigonella  c&rulea ;  and  violet,  Viola  odorata.  It  is 
therefore  evident  that  a  variety  of  dicotyledonous  plants  may 


FIG.  82.   THE  THIELAVIA  DISEASE  OF  TOBACCO.    (After  G.  P.  Clinton) 
Healthy  and  diseased  root  systems 

be  attacked.    The  leguminous  hosts  are,  however,  most  numerous, 
and  the  fungus  is  quite  frequent  on  garden  and  sweet  peas. 

Pathological  effects.  Roots  affected  by  the  Thielavia  do  not 
develop  a  normal  root  system,  or  they  may  be  injured  to  such 
an  extent  that  on  pulling  up  an  affected  plant  from  a  moist  soil 
practically  everything  except  a  stub  of  a  root  will  be  broken  off. 
In  the  case  of  the  tobacco  a  cluster  of  new  roots  may  form  on 
the  crown  above  the  first  injuries  (Fig.  82).  The  fungus  is  ap- 
parently most  injurious  in  the  seed  beds.  Affected  plants  may 
not  be  killed,  and  many  go  through  the  season  with  a  stunted 
growth,  or  with  such  a  check  upon  vigorous  development  at  the 


212 


FUNGOUS  DISEASES  OF  PLANTS 


outset  as  to  cause  manifest  loss  in  the  final  crop.    Again,  diseased 
plants  may  entirely  recover. 

The  surfaces  of  diseased  roots  may  be  roughened  and  browned 
by  the  presence  of  the  fungus,  but  the  tissues  within  are  usually, 
in  the  case  of  violets,  peas,  etc.,  tinted  red  or  pink.  Ordinarily 
the  fungus  penetrates  all  parts  of  the  rootlet,  but  as  is  common 
with  plants  which  are  not  vigorous  or  obligate  parasites,  there  are 
no  abnormal  cell  divisions  of  the  host. 

Morphology  of  the  fungus.  The  mycelium  is  intercellular, 
abundantly  septate,  and  at  first  hyaline.  The  threads  are  narrow, 

and  the  branches  are  cut  off  by  a 
septum  at  a  slight  distance  from 
the  main  hypha,  somewhat  as  in 
Rhizoctonia  (Corticium  vagum). 
Three  kinds  of  spores  have 
been  commonly  found,  namely, 
(i)  endosporous  conidia;  (2)  thick- 
walled  conidia,  .or  chlamydo- 
spores ;  and  (3)  ascospores. 

i.  The  endospores  are  an 
interesting  type  of  spores  formed 
in  chains  in  terminal  branches  or 
clusters  of  branches  (Fig.  83,  a). 
These  spores  are  formed  by  basi- 
petal  septation  as  short  cylindrical 
cells  within  the  branch.  The  tip 
of  the  branch  is  finally  broken 
and  they  are  pushed  out  by  os- 
motic force,  the  branch  assuming  the  part  of  a  spore  case.  The 
endospores  are  distinctly  hyaline,  and  as  produced  in  artificial  cul- 
tures, they  may  remain  united  in  short  threads,  or  cohere  laterally 
as  small  rafts.  Individuals  measure  about  10—20  x  4-5  P- 

2 .  The  chlamydospores  are  thick  walled,  more  or  less  cy- 
lindrical, brown  spores,  borne  in  chains,  the  early  stages  of  for- 
mation differing  apparently  only  in  size  from  the  endospores. 
At  maturity,  however,  the  short  chains,  or  rather  the  colored 
spore  cells  of  these,  break  up,  as  shown  in  Fig.  83,  b,  measuring 
about  12  fi  in  width. 


FIG.  83.    CONIDIA   AND   CHLAMYDO- 
SPORES OF  THIELAVIA 


ASCOMYCETES 


213 


3.  The  perithecia  bearing  the  ascospores  are  relatively  simple. 
The  asci  are  evanescent,  and  the  spores  unicellular,  lenticular, 
vacuolate,  and  measure  about  12  x  5  p. 

Artificial  cultures  are  readily  made  on  various  media,  and 
the  first  two  spore  stages  may  be  quickly  produced  in  culture, 
the  endospores,  particularly,  being  aerial.  The  association  of  the 
ascosporous  stage  with  the  others  and  the  apparent  continuity 
of  mycelium  are  believed  to  show  genetic  connection. 

Control.  Since  the  seed  bed  is  perhaps  the  greater  source 
of  trouble  in  the  case  of  tobacco,  sterilization  of  the  soil  where 
the  disease  has  become  established  may  be  necessary.  Diseased 
plants  should  not  be  used  for  planting.  Thorough  aeration  of 
the  soil  by  drainage  and  cultivation  is  also  desirable.  The  sug- 
gestion that  this  fungus  is  constantly  associated  with  an 'alkaline 
soil  requires  an  investigation  of  the  soil  conditions  with  a  view  to 
correcting  this  by  subsequent  fertilization. 

XX.    SOOTY  MOLD  OF  ORANGE 
Meliola  Camellia  (Catt.)  Sacc. 

FARLOW,  W.  G.  On  a  Disease  of  Olive  and  Orange  Trees,  occurring  in  Cali- 
fornia in  the  Spring  and  Summer  of  1895.  Built,  of  the  Bussey  Institu- 
tion 5  :  404-414.  1876. 

WEBBER,  H.  J.  Sooty  Mold  of  the  Orange  and  Its  Treatment.  Div.  Veg. 
Phys.  and  Path.,  U.  S.  Dept.  Agl.  Built.  13:  1-34.  pis.  /-j.  1897. 

Distribution  and  effects.  The  sooty  mold  is  a  disease  which  is 
probably  distributed  throughout  all  moist  citrus-growing  regions. 
It  is  perhaps  most  injurious  upon  the  orange,  but  it  occurs  also 
upon  the  other  cultivated  citrous  fruits.  In  one  sense  it  is  scarcely 
to  be  regarded  as  a  fungous  disease,  since  the  fungus  which  pro- 
duces the  obnoxious  effect  is  probably  not  parasitic.  Nevertheless, 
the  fruit  infested  by  the  sooty  mold  is  seriously  injured  from  the 
commercial  standpoint,  and  since  it  is  the  fungus  which  effects 
this  injury,  it  may  justly  be  considered  in  this  connection. 

The  sooty  mold  consists,  as  the  name  implies,  of  a  sooty 
growth,  or  crust,  which  occurs  both  upon  leaves  and  fruit.  It 
may  appear  in  isolated  patches  or  investing  practically  the  entire 
leaf  or  fruit  surface.  The  black  mass  is  made  up  entirely  of 
fungous  hyphae.  The  fungus  is  only  found  following  the  attack 


214  FUNGOUS  DISEASES  OF  PLANTS 

of  certain  scale  insects.  In  Florida  it  commonly  succeeds  attacks 
by  the  white  fly,  or  Aleyrodes.  It  is,  however,  in  other  localities 
equally  as  abundant  following  other  species  of  aphid-like  insects. 
The  fungus  has  long  been  a  nuisance  in  the  Mediterranean 
orange  groves,  and  for  some  years  has  been  of  sufficient  abun- 
dance in  both  Florida  and  California  to  require  control  measures. 

The  fungus.  The  mycelium  of  the  fungus  consists  of  large 
branched  threads  which  are  at  first  olive  green  and  velvety,  be- 
coming with  age  deep  brown  with  a  tendency  to  scale  or  break 
up  into  small  patches.  The  hyphae  are  closely  septate,  often  con- 
sisting of  chain-like  groups  of  cells,  readily  separated  one  from 
another.  Moreover,  abundant  branching  and  cementing  together 
of  these  branches  may  give  rise  to  a  kind  of  false  stratum  or 
tissue ;  anastomosing  also  occurs.  Careful  microscopic  examina- 
tion has  failed  to  disclose  any  penetration  of  the  host  by  this 
organism,  and  it  would  appear  that  it  utilizes  as  a  source  of 
nutriment  only  the  so-called  honeydew  resulting  from  the  pres- 
ence of  the  insects  referred  to.  Certain  modified,  knob-like 
branches  of  the  hyphae  are  commonly  found,  but  it  is  apparent 
that  these  hyphopodia  serve  merely  as  organs  of  attachment. 

The  propagative  stages  of  this  fungus  are  numerous.  Conidia 
of  several  types,  stylospores  in  pustules,  pycnidia,  and  perithecia 
may  be  present.  The  conidia  may  be  simple  cells  abscised  from 
upright  hyphae  or  they  may  be  more  highly  differentiated  compound 
structures.  The  stylospores  are  produced  from  small  conidiophores, 
developed  within  peculiar,  elongate,  flask-shaped  structures.  These 
form  a  conspicuous  part  of  the  fungus  and  are  present  throughout 
a  considerable  period  of  its  growth.  They  are  particularly  evident 
when  branched  or  variously  subdivided,  or  adherent  in  groups. 
The  pycnidia  are  relatively  minute,  but  they  occur  in  considerable 
number  distributed  over  the  entire  surface.  The  spherical  perithecia 
are  somewhat  larger  than  the  pycnidia  and,  like  those  of  other 
members  of  this  family,  are  closed  bodies  which  disseminate  their 
spores  only  upon  disintegration.  The  perithecium  may  contain 
several  short,  stout  asci  with  eight  dark,  elliptical,  three-to-four 
septate  spores.  With  the  diverse  sorts  of  spore  forms  mentioned, 
it  will  be  evident  that  the  fungus  is  rapidly  distributed,  and  conse- 
quently spreads  with  alarming  facility  under  favorable  conditions. 


ASCOMYCETES  215 

Control.  A  thorough  study  of  effective  methods  of  control  has 
been  made  under  conditions  in  Florida,  and  it  has  been  found 
that  the  most  effective  preparation  there  tested  is  the  resin  wash. 
This  mixture  consists,  according  to  Webber,  of  the  following 
ingredients  : 

Resin 20  Ib. 

Caustic  soda,  98  per  cent 4  Ib. 

Fish  oil,  crude 3  Ib. 

Water  to  make "...      15  gal. 

He  prepares  this  mixture  as  follows  :  Place  the  resin,  caustic  soda, 
and  fish  oil  in  a  large  kettle.  Pour  over  them  1 3  gallons  of  water, 
and  boil  until  the  resin  is  thoroughly  dissolved,  which  requires  from 
three  to  ten  minutes  after  boiling  has  commenced.  While  hot  add 
enough  water  to  make  just  1 5  gallons.  It  is  advised  to  make  about 
two  sprayings  when  the  insect  is  in  the  larval  stage.  In  Florida, 
winter  sprayings  are  important,  but  a  spraying  in  May  is  also  often 
desirable.  In  all  cases  dilute  the  stock  solution  with  9  parts  of 
water. 

XXI.    ERYSIPHACE^ 

BURRILL,  T.  J.,  and  EARLE,  F.  S.    Parasitic  Fungi  of  Illinois.    111.  State  Lab. 

Nat.  Hist.  2:  387-432.    1887. 
DE  BARY,  A.    Beitrage  zur  Morphologic  u.  Physiologic  der  Pilze  1  (13-14): 

23-75.  pis.  9-12. 
HARPER,  R.  A.    Die  Entwickelung  des  Peritheciums  bei  Sphaerotheca  Cas- 

tagnei  Ber.  d.  deut.  bot.  Ges.  13:  475-481.  pi.  39.    1895. 
HARPER,  R.  A.    Sexual  Reproduction  and  the  Organization  of  the  Nucleus  in 

Certain  Mildews.    Carnegie  Institution  of  Washington.    Publ.  37 :  104. 

7  pis.  1905. 
NEGER,  F.  W.    Beitrage  zur  Biologic  der  Erysipheen.    Flora  90 :  221-272. 

1902. 
REED,  G.  M.    Infection  Experiments  with  Erysiphe  graminis  De  C.    Trans. 

Wis.  Acad.  Sci.,  etc.,  15:    135-162.    1905. 
REED,  G.  M.    Infection  Experiments  with  the  Mildew  on  Cucurbits,  Erysiphe 

Cichoracearum  De  C.    Trans.  Wis.  Acad.  Sci.,  etc.,  15:   527-547.    1907. 
SALMON,  E.  S.    A  Monograph  of  the  Erysiphaceae.    Memoirs  of  the  Torrey 

Bot.  Club  9  :  292pp.    9  pis.    1900. 
SALMON,  E.  S.    Further  Cultural  Experiments  with  Biologic  Forms  of  the 

Erysiphaceae.    Ann.  Bot.  19  :    125-148.    1905. 
SANDS,  M.  C.    Nuclear  Structures  and  Spore  Formation  in  Microsphaera  Alni. 

Trans.  Wis.  Acad.  Sci.,  etc.,  15:   733-752.  pi.  46.    1907. 
SMITH,  GRANT.    The  Haustoria  of  the  Erysipheae.    Bot.  Gaz.  29:   153-184. 

pis.  n,  12.    1900. 

This  is  a  family  which,  according  to  the  most  recent  mono- 
graph, includes  forty-nine  species  and  eleven  varieties  of  fungi, 


2l6  FUNGOUS  DISEASES  OF  PLANTS 

commonly  known  as  mildews,  powdery  mildews,  and  blights 
(Germany,  Mehltau ;  France,  blanc,  etc.).  Some  writers  would 
make  more  than  a  hundred  species  of  the  various  forms,  the 
species  being  determined  very  largely  by  the  hosts  upon  which 
they  occur.  The  Erysiphaceae  are  all  strictly  parasitic,  producing 
a  considerable,  septate,  superficial  mycelium  with  a  single  form 
of  conidial  spore  and  a  closed  perithecium  containing  the  asci. 
This  family  is  such  a  homogeneous,  coherent  group  that  it  may 
be  treated  as  a  whole,  and  subsequently  a  few  notes  on  particularly 
important  species  may  be  made. 

Geographical.  The  various  members  of  this  family  are,  gener- 
ally speaking,  most  abundant  in  the  north  temperate  regions  of 
the  earth,  but  as  a  family  they  are  not  limited  in  their  distribu- 
tion. Moreover,  one  species  is  known  to  occur  as  far  north  as 
Greenland,  while  another  is  found  in  Terra  del  Fuego.  The 
number  of  species  common  to  America,  on  the  one  hand,  and  to 
Europe,  Asia,  and  Africa,  on  the  other,  is  approximately  the  same  ; 
but  there  are  supposedly  more  endemic  forms  in  America  than  in 
all  other  countries.  Salmon  gives  fourteen  endemic  species  with 
five  varieties  for  America,  while  only  thirteen  species  and  four 
varieties  are  known  to  be  endemic  in  Europe,  Asia,  and  Africa 
combined. 

Climatic  relations.  The  distribution  of  these  fungi  is  ap- 
parently not  closely  restricted  by  slight  climatic  differences.  A 
certain  amount  of  moisture  is  unquestionably  essential  to  the 
vigorous  production  of  the  superficial  mycelium  characteristic 
of  this  group,  and  there  are  fewer  species  in  dry,  exposed 
regions,  as,  for  instance,  in  the  Great  Plains  regions  of  the 
United  States,  than  in  the  more  moist  Appalachian  region. 
Nevertheless,  there  are  a  number  of  species  that  may  be  found 
from  the  extreme  north  to  the  extreme  south,  as  well  as  from 
east  to  west  in  both  the  eastern  and  western  continents.  Climatic 
conditions,  especially,  may  determine  whether  or  not  a  particu- 
lar species  may  become  a  devastating  disease-producing  organism 
or  may  be  classed  merely  as  a  fungus  of  occasional  economic  im- 
portance. Erysiphe  graminis,  for  instance,  is  seldom  a  fungus  of 
any  consequence  in  most  sections  of  the  United  States,  while  in 
England  it  may  at  times  cause  serious  injury  to  cultivated  grasses, 


ASCOMYCETES  2 1 7 

Host  plants.  The  various  species  and  varieties  of  mildew  have 
been  reported  upon  about  fifteen  hundred  species  of  phanerogams. 
The  list  of  hosts  includes  plants  of  numerous  orders  and  families. 
A  few  notable  exemptions  among  plants  of  normal  terrestrial 
habits  are  Liliaceae,  Iridaceae,  and  some  other  monocotyledons. 
Furthermore,  there  are  many  exceptions  among  such  families,  for 
instance,  those  having  the  habit  of  growing  under  unusually  moist 
conditions.  Moreover,  herbs,  shrubs,  and  trees  are  more  or  less 
equally  affected,  and  sometimes  a  single  species  of  these  mildews 
may  be  found  upon  plants  of  all  three  sorts. 

The  leaves  are  usually  the  chief  parts  affected,  although  some 
species  may  attack  also  the  twigs,  stems,  and  fruits.  As  a  rule, 
those  having  the  densest  mycelia  are  more  persistent  and  more 
likely  to  infest  all  portions  of  the  plant.  The  Erysiphaceae  seldom 
cause  conspicuous  distortions  of  the  host  plant.  The  anatomical 
modifications  are  therefore  secondary  in  interest  to  the  physio- 
logical effects. 

Cross  inoculations.  In  a  very  recent  summary  of  the  general 
results  of  cross  inoculation  in  the  mildews,  Reed  states : l 

One  or  more  species  of  five  of  the  genera  of  the  Erysiphacese  have  been 
tested  for  their  capacity  for  infecting  host  plants  other  than  the  one  from  which 
they  came.  Podosphaera  is  the  only  genus  which  thus  far  has  not  been  tested. 
With  reference  to  four  genera,  Microsphaera,  Sphaerotheca,  Phyllactinia,  and 
Uncinula,  the  data  are  very  meager.  The  bulk  of  the  work  has  been  done  with 
three  species  of  Erysiphe,  —  E,  Cichoracearum,  E.  graminis,  and  E.  Poly- 
goni.  Even  with  these  species  the  number  of  trials  is  very  small  in  many 
cases,  the  evidence  often  resting  on  a  single  experiment.  Still,  sufficient  data 
have  been  accumulated  to  form  the  basis  of  certain  at  least  tentative  general 
conclusions. 

So  far  as  investigated,  the  mildew  on  the  cucurbits,  Erysiphe  Cichorace- 
arum D.  C,  is  the  only  one  which  is  shown  to  be  capable  of  infesting  plants 
belonging  to  more  than  one  genus.  My  results  with  this  mildew  are  based  on 
a  large  number  of  trials,  many  of  them  repeated  at  different  times  during  three 
years,  and  cannot  be  questioned. 

There  are  other  cases  where  the  mildew  is  limited  closely  to  plants  of  a  single 
genus.  For  example,  the  mildew  on  rye  is  limited  to  species  of  the  genus  Secale. 
The  same  is  true  with  reference  to  the  bluegrass  mildew  on  species  of  Poa. 

Several  cases  also  are  recorded  where  the  mildew  from  one  species  will  not 
infect  other  species  of  the  same  genus.  Most  of  these  claims,  however,  rest  on 

1  Reed,  Geo.  M.    Infection  Experiments  with  Erysiphe  cichoracearum  PC- 
of  Wisconsin  Built.  350  :  340-416.    10,08, 


218 


FUNGOUS  DISEASES  OF  PLANTS 


insufficient  data.  The  evidence  is  more  conclusive  with  reference  to  the  mil- 
dew on  species  of  Hordeum  and  also  the  one  on  the  Brome  grasses.  Salmon 
.  .  .  has  investigated  both  of  these.  The  mildew  on  barley  (Hordeum  vul- 
gare]  will  infect  this  species  and  also  Hordeum  distichum,  H.  decipiens, 
H.  Hexastichum,  H.  intermedium,  and  H.  Zeocriton,  but  will  not  pass 
over  to  Hordeum  jubatum,  H.  bulbosum,  H.  murinum,  H.  secalinum, 
H.  sylvaticum.  In  some  of  these  cases,  however,  the  number  of  trials  is 
very  small. 

Morphological.    With    only   one    or    two    exceptions    (notably 
Sph&rotheca  Mors-uvce)  the  superficial  mycelium  of  these  plants 

consists  of  colorless  hyphae, 
considerably  septate,  each 
cell  being  ordinarily  uninu- 
cleate.  In  all  species  except 
two,  so  far  as  is  known,  the 
haustoria  penetrate  the  epi- 
dermal cells  in  the  form 
of  short,  swollen  branches. 
However,  in  one  common 
mildew  of  shrubs  and  trees 
(Phyllactinia  Coryled)  hy- 
phal  branches  grow  through 
the  stomata  and  into  the 
intercellular  spaces.  These  branches  may  in  turn  develop  haustoria, 
which  enter  the  cells  in  contact  with  this  intercellular  hypha.  As  a 
rule  conidial  production  in  all  forms  begins  whenever  a  con- 
siderable mycelium  has  been  developed.  These  conidia  consist, 
quite  generally,  of  a  single  chain  of  cylindrical  or  more  or  less 
barrel-shaped  unicellular  portions  produced  in  basipetal  order  on 
short,  erect  conidiophores,  developed  directly  from  a  hyphal  cell. 
The  conidia  are  capable  of  immediate  germination,  and  since 
they  are  produced  in  quantity,  they  frequently  give  the  mealy 
or  powdery  appearance  to  the  parts  affected.  They  serve  for  the 
rapid  propagation  of  these  fungi.  The  conidial  stage  was  for  a 
long  time  unconnected  with  the  perithecium  form  and  was  then 
known  under  the  form-generic  name  Oidium.  The  minute  char- 
acteristics of  the  oidial  stages  have  not  been  sufficiently  studied. 
It  is  proper  to  use  the  name  Oidium  for  any  conidial  form  the 
perfect  stage  of  which  is  unknown  or  indetermined. 


FIG.  84.   HABIT  OF  A  POWDERY  MILDEW 


ASCOMYCETES 


2I9 


middle  or  latter 


Perithecia  are  usually  developed  dflru 

part  of  the  growing  season.  They  ^re^Jroduced  directly  upon 
the  mycelium,  and  the  development  is  interesting  and  instructive. 
The  development,  however,  can  be  best  followed  only  by  s6#rf 
sections  of  properly  imbedded  material.  In  brief,  it  m^y>  be 
described  as  follows  :  Two  adjacent  cells  or  hyphae  give  rise  to 
erect  branches,  one  of  which  is  larger  and  may  be  designated 
as  the  oogonium,  the  other,  smaller  branch  as  the  antheridium. 
After  a  basal  cell  is  cut  off  in  each  case,  and  further,  a  terminal 
antheridial  cell  in  the  one  case,  there  is  dissolution  of  a  portion 


FIG.  85.    PHYLLACTINIA  CORYLEA:    GAMETES,    FERTILIZATION,  AND 
DEVELOPMENT  OF  PERITHECIUM  AND  YOUNG  ASCI.    (After  Harper) 

of  the  wall  between  the  antheridium  and  the  oogonium,  migration 
of  the  antheridial  nucleus,  and  fusion  of  this  with  the  oogonial 
nucleus  (Fig.  85,  b).  Subsequently  the  oogonial  cell  undergoes  sev- 
eral divisions.  The  last  cell  but  one  in  this  ascogonium  contains 
always  two  nuclei,  and  these  fuse  prior  to  the  development  of  this 
cell  as  an  ascus.  This  is  the  case  when  a  single  ascus  is  produced, 
and  it  is  only  slightly  more  complex  when  many  asci  result  (cf . 
Fig.  85,  d-f}.  Following  the  fusion  of  the  two  gametic  nuclei, 
hyphal  branches  arise  from  the  stalk  cell  of  the  oogonium.  These 
converge  around  the  oogonium  and  finally  completely  inclose 
it.  Within  this  first  layer  a  second  layer  of  hyphae  is  produced 
in  similar  manner ;  and  subsequently,  by  outgrowths  from  each  of 


220 


FUNGOUS  DISEASES  OF  PLANTS 


these  layers  into  all  available  space,  smaller  hyphae  are  protruded ; 
thus  a  compact  inclosing  body  or  perithecium  is  developed.  With 
the  further  growth  of  the  perithecium  and  the  increase  in  size 
of  the  ascus,  the  inner  layer  and  all  internal  hyphal  branches 
are  dissolved  and  appropriated.  Meanwhile,  the  outer  layer  be- 
comes yellow  or  brown  and  forms  the  true  wall  of  the  peri- 
thecium. From  the  wall  cells  of  the  perithecium  there  are 


FIG.  86.    SPORE  FORMS  AND  APPENDAGES  OF  ERYSIPHACE^E 

«,  Eryslphe  Polygoni  ;  b,  Podosphara  Oxyacanthce  ;  c,  Microsphcera  Alni ;  e,  Phyllactinia 
Coiylea ;  d  and  /,  Uncinula  nee  at  or 

produced,  either  from  the  base  or  from  a  more  or  less  equatorial 
plane,  the  characteristic  appendages.  In  a  few  cases  only  are 
appendages  produced  from  the  apex.  At  maturity  there  are  one 
or  more  asci,  depending  upon  the  genus,  and  each  ascus  con- 
tains normally  from  two  to  eight  spores,  the  shape  of  the  ascus 
varying  from  practically  spherical  in  the  one-ascus  forms  to 
clavate  or  cylindrical  where  there  are  two  or  many  asci.  The 
spores  are  one  celled  and  colorless.  As  a  rule  the  ascospores 
do  not  germinate  immediately,  requiring  a  period  of  rest.  By 


ASCOMYCETES  221 

the  following  spring  the  perithecia  are  very  brittle  and  are  said 
to  break  open  forcibly  in  water,  after  which  time  the  ascospores 
readily  germinate.  The  appendages  of  the  perithecium  are  very 
different  in  structure  from  the  mycelium  in  general.  The  thick 
walls,  rigidity  of  the  cells  in  most  genera,  and  peculiar  branching 
indicate  that  they  are  specialized  structures,  and  they  doubtless 
have  an  importance  in  relation  to  the  support  of  the  perithecium 
or  the  dissemination  of  this  body. 

Classification.  The  generic  subdivisions  are  based  upon  the 
number  of  asci  in  the  perithecium  and  upon  the  form  and 
method  of  branching  of  the  appendages.  The  following  key  will 
indicate  the  chief  generic  characters  : 

A.  Perithecia  contain  a  single  ascus. 

1 .  Appendages  simple,  flexuous,  and  undivided  at  the  tip. 

Sphcerotheca 

2.  Appendages  once  or  more  dichotomously  divided  at  the  tip. 

Podosphczra 

B.  Perithecia  containing  several  to  many  asci. 

1 .  Appendages  never  more  than  slightly  swollen  at  the  base. 

a.  Appendages  simple  or  more  or  less  flexuous,  or  irreg- 

ularly branched,  mycelial-like ;   without  tip  peculiar- 
ities  Erysiphe 

b.  Appendages  usually  straight,   once    or   more  dichoto- 

mously branched  at  the  tip   .     .     .     .  Microsphara 

c.  Appendages  usually  straight  and  spirally  inrolled  at  the 

tip '."    Uncinula 

2.  Appendages  swollen  at  the  base  so  as  to  form  an  enlarged  plate. 

Phyllactinia 

XXII.    THE  GOOSEBERRY  MILDEW 
Sphcerotheca  Mors-uvce  (Schw.)  B.  &  C. 

CLOSE,  C.  P.    Treatment  for  Gooseberry  Mildew.    N.  Y.  (Geneva)  Agl.  Exp. 

Sta.  Built.  161 :    153-164.  pis.  1-2.    1899. 
ERIKSSON,  J.    Der  amerikanische  Stachelbeermehltau  in  Europa,  seine  jetzige 

Verbreitung  und  der  Kampf  gegen  ihn.    Zeitsch.  f.  Pflanzenkr.  16 :  83- 

90.    1906. 
SALMON,  E.  S.    On  the  Present  Aspect  of  the  Epidemic  of  the  American 

Gooseberry  Mildew  in  Europe.    Journ.  Roy.  Hort.  Soc.  29:    102-110. 
fig.  23.    1905. 

This  species  has  long  been  known  as  the  cause  of  an  im- 
portant disease  of  gooseberries  in  the  United  States.  It  occurs 


222 


FUNGOUS  DISEASES  OF  PLANTS 


upon  the  leaves  and  stems,  but  particularly  upon  the  berries  of 
the  host,  and  it  may  sometimes  cause  injury  to  currant  bushes. 
The  mycelium  is  more  persistent  than  that  of  most  Erysiphaceae. 
It  is  one  of  the  few  forms  the  mycelium  of  which  becomes  buff 


FIG.  87.   GOOSEBERRY  MILDEW.    (After  Close) 

or  brown  and  thick- walled  with  age.  The  mycelium  forms  dense 
circular  or  effuse  patches,  sometimes  completely  covering  a  berry 
and  the  adjacent  twig. 

The  perithecia  are  imbedded  in  the  dense  mycelium.  They 
average  about  80-100 /A  in  diameter  and  are  beset  with  a  few 
light  brown,  tortuous  appendages.  A  single  subglobose  ascus 


ASCOMYCETES 


223 


contains  relatively  large  spores.  According  to  Salmon  this  species 
is  indistinguishable  from  the  Sphaerotheca  found  in  Europe  upon 
Euphorbia.  The  latter  is,  however,  not  very  common  in  Europe. 
During  the  summer  of  1906  a  serious  outbreak  of  gooseberry 
mildew  was  reported  in  Europe.  The  fungus  has  spread  rapidly, 
and  the  result  of  this  outbreak  will  undoubtedly  afford  European 


FIG.  88.    MILDEW  OF  PEACH  ON  NURSERY  STOCK 

investigators  an  opportunity  of  testing  the  validity  of  the  above 
opinion. 

Control.  The  American  gooseberry  mildew  is  one  of  the  most 
difficult  of  the  mildews  to  control.  English  varieties  of  goose- 
berries in  America  have  proved  most  susceptible,  and  the  best 
results  have  been  obtained  by  the  use  of  a  spray  of  relatively 
strong  potassium  sulfide,  —  I  ounce  to  2  gallons  of  water.  Spray- 
ing should  be  given  from  the  time  that  the  buds  break  open,  and 


224 


FUNGOUS  DISEASES  OF  PLANTS 


where  the  fungus  promises  to  be  abundant,  it  may  be  necessary 
to  repeat  the  spray  every  ten  or  twelve  days.  Recently  it  has 
been  reported  that  sulfuric  acid  may  be  used  to  advantage  in  the 
treatment  of  the  rose  mildew,  the  strength  employed  being  I  part 
of  strong  acid  to  1000  parts  of  water.  This  preparation  should 
prove  serviceable,  but  it  has  not  been  tested  for  the  gooseberry 
mildew.  Winter  treatment  with  a  lime-sulfur  wash  has  been  con- 
sidered desirable  as  a  result  of  some  Canadian  experiments. 


XXIII.    MILDEW  OF  PEACH.    ROSE  MILDEW 
Sphczrotheca  pannosa  (Wallr.)  Lev. 

SMITH,  ERW.  F.    Peach  Mildew.    Journ.  Mycology  7 :  90-91.    1892. 
WHIPPLE,  O.  B.    Peach  Mildew.    Colo.  Agl.  Exp.  Sta.  Built.  107:    1-7.  pis. 

7,  2.     1906. 

This  mildew  bears  the  relation  to  the  peach  that  Podosphcera 
leucotricha  bears  to  the  apple,  that  is,  it  is  more  commonly  found 

on  nursery  stock,  and 
then  usually  only  when 
the  conditions  are  moist 
and  the  stock  crowded, 
although  occasionally  it 
occurs  on  mature  trees 
(Figs.  88  and  89). 

It  is  as  a  disease  of 
cultivated  roses  that  this 
fungus  is  best  known, 
and  most  destructive.  It 
is  widely  distributed  and 
indeed  absent  from  very  few  home  gardens.  There  is  great  differ- 
ence in  the  susceptibility  of  different  varieties  of  the  rose,  and  selec- 
tion should  lead  to  resistant  strains  in  many  cases.  The  crimson 
rambler  is  notably  sensitive. 

This  mildew  covers  the  leaves,  especially  the  young  leaves  and 
the  vigorous  and  young  shoots,  injuring  and  often  arching  or 
curling  the  leaves  and  deforming  the  more  succulent  stems. 
The  oidial  stage  is  produced  in  great  profusion,  and  consequently 
the  disease  spreads  rapidly.  Perithecia  are  not  always  present. 


FIG.  89.   MILDEW  ON  PEACHES 


ASCOMYCETES 


225 


Following  a  moist  early  summer  I  have  found  the  perithecia  abun- 
dant on  old  leaves  in  the  shade  during  a  very  dry  period  in  late 
summer  (Fig.  90). 

Control.    Thorough  dusting  with  flowers  of  sulfur  every  ten  days 
is  often  sufficient.    Ammoniacal  copper  carbonate  is  also  effective. 


FIG.  90.    ROSE  MILDEW,  PERITHECIA  PRESENT 

Sulfuric  acid  i  to  1000  has  recently  been  recommended.  No  ex- 
periments have  been  reported  respecting  the  use  of  the  "  self- 
cooked  "  lime-sulfur  for  the  rose  mildew,  but  there  is  reason  to 
believe  that  it  may  be  far  more  effective  than  sulfur  in  this  case. 


226  FUNGOUS   DISEASES  OF  PLANTS 

XXIV.    MILDEW  OF  APPLE  AND  CHERRY 
Podosphcera  Oxyacanthce  (De  C.)  De  Bary 

FAIRCHILD,  D.  G.    Experiments  in   Preventing   Leaf   Diseases  of   Nursery 
Stock.    Journ.  Mycology?:   256.  1894. 

This  fungus  is  common  on  a  large  number  of  rosaceous  and 
other  plants,  including  apples,  plums,  thorn  apples,  etc.    It  may 


FIG'.  91.   SPHALROTHECA  HUMULI  ON  CULTIVATED  STRAWBERRY 
(Photograph  by  E.  H.  Favor) 

be  considered  as  a  destructive  disease  in  this  country  chiefly  as 
it  occurs  upon  apple  nursery  stock  or  upon  the  cherry  (Fig.  92). 
Upon  the  young  apple  plants  the  mycelium  is  rather  dense  and 
persistent.  Perithecia  are  from  65  to  90  /-i  in  diameter  and  the 
appendages,  from  4  to  30  in  number,  are  usually  from  I  to  5 
times  as  long  as  the  diameter  of  the  perithecia.  Throughout 
about  half  of  the  length  of  the  appendages  they  are  dark  brown 
in  color,  and  they  are  also  several  times  dichotomously  branched 
at  the  tip.  A  single  ascus  is  given  as  58  to  90  by  45  to  75  /x,  con- 
taining normally  8  spores.  It  is  believed  that  the  injurious  action 
of  this  fungus  may  be  easily  prevented  by  the  use  of  copper 
sprays. 

Podosphaera  leucotricha  (Ell.  and  Ev.)  Salm.    In  nurseries  of 
New  York  and  other  eastern  states  this  fungus  has,  during  moist 


ASCOMYCETES 


227 


seasons,  given  trouble  of  serious  nature,  particularly  where  the 
nursery  stock  are  planted  very  close  together.  The  mildew  covers 
both  surfaces  of  the  leaves  and  frequently  involves  the  whole 
twig.  Spraying  with  Bordeaux  mixture  and  potassium  sulfide  is 
effective. 

XXV.    POWDERY  MILDEW  OF  PEAS 
Erysiphe  Polygoni  De  C. 

This  fungus  is  distributed  throughout  the  world.    It  is  the  most 
common  and  one  of  the  most  variable  of  the  Erysiphaceae.    The 
species   has   been   listed   upon  -con- 
siderably more  than  three  hundred 
hosts  of  diverse  genera  and  orders. 
Among  these  the  succulent  and  her- 
baceous plants  predominate,  but  the 
fungus    occurs   upon    some    woody 
hosts. 

As  a  mildew  of  garden  peas  (Pisum 
sativum)  this  fungus  may  become  a 
nuisance,  especially  when  an  attempt 
is  made  to  grow  these  plants  during 
the  late  summer.  It  is  most  preva- 
lent during  moist  seasons,  and  more 
destructive  in  some  Atlantic  and 
southern  states.  Upon  this  host  the 
fungus  forms  a  rather  dense,  persist- 
ent mycelium,  frequently  covering 
stems,  leaves,  and  pods.  The  co- 
nidia  are  developed  in  profusion,  The 
perithecia,  averaging  90/1.  in  diam- 
eter, are  also  produced  in  large  num- 
ber during  a  later  period,  commonly 
after  the  plants  have  begun  to  dry 
up.  When  the  mildew  attacks  young  plants  the  crop  is  generally  a 
total  loss.  The  fungus  also  attacks  beans  and  certain  vetches. 

The  perithecia  contain  ordinarily  6-8  asci,  each  with  2-3  spores. 
The  appendages  are  very  variable,  even  upon  the  same  host,  under 
similar  conditions, 


FIG.  92.    MILDEW  OF  CHERRY 


228 


FUNGOUS  DISEASES  OF  PLANTS 


XXVI.    MILDEW  OF  COMPOSITES  AND  OTHER  PLANTS 
Erysiphe  Cichoracearum  De  C. 

This  species  of  mildew  is  also  widely  distributed  and  occurs 
upon  more  than  two  hundred  hosts  of  numerous  families.    It  is 

unusually  common  upon  spe- 
cies of  Compositae  and  in 
general  is  easily  the  most 
destructive  fungus  of  these 
hosts.  It  is  also  well  known 
to  the  florist  upon  species 
of  phlox  and  to  the  gar- 
dener upon  some  varieties 
of  cucurbits. 

The  fungus  is  often  con- 
fused with  the  previous  spe- 
cies. The  perithecia  are 
about  equal  in  size,  but  the 
appendages  of  this  form 
are  usually  short.  The  asci 
are  numerous  (often  10-15), 
and  Salmon  considers  that 
the  central  specific  charac- 
ter lies  in  the  possession  of 
two  spores.  Nevertheless, 
this  species  is  also  variable 
in  every  character,  and  it 
will  not  be  easy  to  distin- 
guish morphologically  between  certain  forms  of  the  two  species. 


FIG.  93.   MICROSPH&RA  ALNI,  PERSISTENT 

FORM  ON  OAK.    (Photograph  by  Geo.  F. 

Atkinson) 


XXVII.    MILDEW  OF  WOODY  PLANTS 

Microsphara  Alni  (Wallr.)  Wint. 

This  variable  species  is  typically  a  fungus  of  a  variety  of 
woody  plants.  It  is  common  upon  amentiferous  trees  and  shrubs, 
but  popularly  is  doubtless  best  known  as  the  lilac  or  syringa 
mildew.  Upon  the  lilac  the  mycelium  covers  the  entire  leaf. 
So  constant  is  its  occurrence  upon  this  host  during  the  late 


ASC6MYCETES 


22C) 


Summer  in  the  United  States  that  one  unconsciously  associ- 
ates with  the  lilac,  during  that  season,  a  grayish  color.  Upon 
some  hosts,  however,  the  mycelium  may  form  persistent  patches 
(Fig.  93). 

The  perithecium  is  general-ly  small,  with  appendages  averag- 
ing il  times  its  diameter.  These  are  colorless  to  light  brown  in 
part,  and  3  to  6  times  dichotomously  branched.  The  asci  are 
usually  3-8,  each  containing  4-8  relatively  small  (18-23  X  10- 
12/4)  spores. 

XXVIII.    POWDERY  MILDEW  OF  GRAPE 
Uncinula  necator  (Schw.)  Burr. 

BIOLETTI,  F.  T.    Oidium  or  Powdery  Mildew  of  the  Vine.    Calif.  Agl.  Exp. 

Sta.  Built.  186:   315-352.  figs.  /-//.    1907. 
GALLOWAY,  B.  T.    Observations  on  the  Development  of  Uncinula  spiralis. 

Bot.  Gaz.  20:  486-491.  pi.  32-33.    1895. 
VIALA,  P.    Les  maladies  de  la  vigne,  /.  £.,  2-56.  pi.  z.  figs.  i-ig.    1893. 

This  mildew  is  one  which  has  long  been  known  as  an  im- 
portant fungous  disease  in  Europe  and  in  America.  For  many 
years  it  was  supposed  that  the  American  plant  might  not  be  the 
same  as  the  European,  since  in  the  latter  country  only  the  oidium 
stage  was  known,  that  stage  having  been  described  as  Oidium 
Tuckeri  Berk.  It  is  now  certain  that  the  plant  in  the  two  coun- 
tries is  the  same  species. 

This  species  has  a  light  mycelium,  which  develops  on  both 
sides  of  the  leaves  and  sometimes  on  the  flower  clusters.  In 
the  United  States  it  is  especially  abundant  on  the  leaves  in  moist 
situations  during  the  late  season.  It  produces  a  mottled  and 
slightly  arched  condition.  During  some  seasons  considerable  in- 
jury results  to  the  plant.  The  conidia  are  produced  in  abundance 
and  the  disease  may  be  rapidly  spread.  The  perithecia  vary  from 
70  to  1 28 /A  in  diameter  and  are  provided  with  a  varying  number 
of  appendages,  usually  from  10  to  20  or  more,  each  appendage  be- 
ing from  one  to  four  times  as  long  as  the  diameter  of  the  peri- 
thecium. These  appendages  are  straight  or  slightly  flexuous, 
except  as  to  the  uncinate  or  incurved  tip.  They  may  be  septate, 
and  amber  brown  in  the  lower  half.  There  are  usually  4-6  asci, 
each  containing  4-7  spores. 


2  3o 


FUNGOUS  DISEASES  OF  PLANTS 


It  is  difficult  to  explain  the  absence  of  the  perithecial  stage 
for  co  long  a  period  in  Europe,  and  even  now  when  many 
observers  would  be  alert  to  the  presence  of  such  a  form,  it  is 
certain  that  the  occurrence  of  perithecia  is  exceptional.  For  a 
long  time  it  was  supposed  that  the  disease  was  imported  to 
Europe  from  America,  as  were  other  grape  diseases,  but  since' 
the  fungus  is  also  found  in  Asia,  there  is  no  special  reason  for 
this  assumption.  The  use  of  the  more  common  fungicides  has 
not  been  so  successful  in  preventing  the  attacks  of  this  fungus 
as  the  simple  sulfur  dust  treatment. 

XXIX.    POWDERY  MILDEW  OF  WILLOW  AND  POPLAR 
Uncinula  Salicis  (De  C.)  Wint. 

This  species  is  apparently  limited  in  host  plants  to  the  two 
genera  Salix  and  Populus,  but  it  occurs  upon  many  species  of 

these  throughout  their 
distribution.  The  my- 
celium occurs  on  both 
surfaces,  frequently 
evanescent  on  poplars, 
while  often  persistent 
and  in  patch-like  areas 
on  willow,  or  covering 
the  entire  surface  (Fig. 
94).  On  the  latter  the 
perithecia  are  also  gen- 
erally  aggregated. 
They  average  1 3  5  ^  in 
diameter,  and  are  pro- 
vided with  numerous 
(often  more  than  100) 
hyaline  appendages, 
the  tips  of  which  are 
distinctly  uncinate. 
The  asci  are  generally 
about  10,  with  4-6 
spores,  measuring 


FIG.  94.    POWDERY  MILDEW  OF  WILLOW.    (Photo- 
graph by  Geo.  F.  Atkinson) 


20-26  x  10-15  /i. 


ASCOMYCETES 


231 


On  the  willow  the  area  occupied  by  the  mycelium  sometimes 
shows  a  tendency  to  retain  its  chlorophyll  longer  than  other  por- 
tions of  the  leaf.  This  stimulating  effect  of  a  parasite  is,  however, 
best  marked  in  the  case  of  Uncinula  Aceris  (De  C.)  Wint.,  occur- 
ring on  several  species  of  maple  (Acer).  The  yellow  leaves  in  the 
late  autumn  may  show  definite  green  areas,  which  will  be  found 
to  be  the  parts  of  the  leaf  occupied  by  the  fungus  (Fig.  95). 


XXX.    COMMON  MILDEW  OF  TREES 
Phyllactinia  Corylea  (Pers.)  Karst. 

PALLA,  E.    Ueber  die  Gattung  Phyllactinia.    Ber.  d.  deut.  bot.  Ges.  17 :  64- 

72.  pi.  5.    1899. 
SALMON,  E.  S.    On  Certain  Structures  in  Phyllactinia.    Journ.  Bot.  37 :  449- 

454.  pi.  402.    1899. 

This  species  of  mildew  is  so  distinct  from  those  previously  dis- 
cussed that  it  is  by  some 
made  the  type  of  a  sub- 
family. As  previously 
stated,  no  haustoria  are 
present,  but  special  seta- 
like  branches  penetrate 
the  host.  The  perithecium 
is  large  and  provided  with 
hyaline,  rigid,  acicular  ap- 
pendages, each  with  a  swol- 
len base.  There  are  many 
asci,  containing  2  or  3 
spores  (Fig.  86,  e).  The  de- 
velopment of  the  asci  has 
been  discussed  (Fig.  85). 

This  species  occurs  more 
commonly  upon  shrubs  or 
trees,  but  it  is  also  para- 
sitic upon  a  limited  num- 
ber of  herbaceous  plants. 
It  is  known  to  be  distributed  throughout  the  northern  hemisphere, 
and  is  frequently  one  of  the  more  common  of  the  surface  mildews. 


FIG.  95.    YELLOW   LEAF  OF   MAPLE,   WITH 
GREEN  AREAS  OCCUPIED  BY  UNCINULA 


232  FUNGOUS   DISEASES  OF  PLANTS 

XXXI.  HYPOCREACE^E 

In  this  family  the  mycelium  is  light  or  bright  colored,  never 
dark,  as  is  also  the  stroma  when  present.  Perithecia  are  also 
colored  and  vary  from  a  buff  or  yellow  to  brown,  red,  or  purple, 
never  black.  They  are  usually  more  or  less  flask-shaped,  free 
upon  the  substratum,  borne  upon  a  mycelial  weft  (subiculum), 
upon  a  stroma,  or  imbedded  partially  or  completely  in  a  stroma 
(well-differentiated  perithecial  walls  are  absent  in  Claviceps,  etc.). 
The  perithecium  possesses  a  distinct  ostiolum  or  mouth.  The 
asci  are  cylindrical  or  clavate  fusiform.  The  spores  (usually  eight) 
are  diverse  in  form,  and  they  sometimes  bud  within  the  ascus.  Pa- 
raphyses  may  be  present.  In  general,  the  family  is  distinguished 
from  other  pyrenomycetes  only  by  color  and  texture. 

In  this  large  family  important  pathological  forms  may  be  se- 
lected from  three  genera,  —  Neocosmospora,  Nectria,  and  Claviceps. 

In  Neocosmospora  there  is  no  true  stroma.  The  colored  peri- 
thecia  (buff  or  yellow  to  red)  are  clustered  or  scattered.  They 
possess  pseudoparenchymatous  walls  and  rather  long  ostiola. 
The  asci  contain  eight  spherical,  brown  spores,  with  a  distinctly 
wrinkled  surface.  Conidia  are  present. 

In  the  genus  Nectria  the  perithecia  are  yellowish  to  brown 
or  red,  single  or  grouped,  even  varying  as  to  the  extent  of 
the  stroma,  which  is,  however,  usually  tuberculate  or  wart-like. 
The  asci  are  mostly  cylindrical,  bearing  eight  I -septate,  usually 
hyaline,  elliptical  spores.  Conidia  are  common. 

Claviceps  is  characterized  by  the  development  of  definite  stro- 
mata  (sporophores)  from  a  relatively  large  sclerotium,  a  stroma 
consisting  of  a  sterile  stalk  and  a  fertile  head.  Within  the  latter 
(peripherally  disposed)  the  asci  are  contained  in  flask-shaped 
structures.  There  is  no  definite  perithecial  wall  surrounding  the 
ascal  conceptacle.  The  asci  are  more  or  less  cylindrical  and  bear 
eight  hyaline,  continuous,  needle-shaped  spores. 

Closely  related  to  Claviceps  may  be  mentioned  the  genus  Cor- 
dyceps,  including  some  interesting  and  striking  forms.  The  major- 
ity occur  upon  insects,  upon  which  they  are  parasitic  or  saprophytic. 
Two  species  are  more  or  less  common  parasites  of  Elaphomyces, 
a  truffle-like,  hypogeous  genus. 


ASCOMYCETES  233 

XXXII.    WILT  DISEASE  OF  COTTON,  COWPEA,  AND 
WATERMELON 

Neocosmospora  vasinfecta  (Atkinson)  Erw.  Smith 

ATKINSON,  GEO.  F.    Some  Diseases  of  Cotton.    III.  Frenching.    Ala.  Exp. 

Sta.  Built.  41  :    19-29.    1892. 
ORTON,  W.  A.    The  Wilt  Disease  of  Cotton  and  its  Control.    Div.  Veg.  Phys. 

and  Path.,  U.  S.  Dept.  Agl.  Built.  27:    1-16.  pis.  1-14.    1900. 
ORTON,  W.  A.    The  Wilt  Disease  of  the  Cowpea  and  its  Control.    Bureau  of 

Plant  Industry,  U.  S.  Dept.  Agl.  Built.  17:    1-20.  pis.  1-4.    1902. 
SMITH,  ERW.  F.    Wilt  Disease  of  Cotton,  Watermelon,  and  Cowpea.    Div. 

Veg.  Phys.  and  Path.,  U.  S.  Dept.  Agl.  Built.  17  :    1-53.  pis.  i-io.   1899. 

This  is  a  fungous  disease  which  has  become  prominent  only 
during  the  past  fifteen  years,  and  it  is  already  a  serious  foe.    The 


FIG.  96.   EFFECTS  OF  THE  COTTON  WILT  FUNGUS  IN  A  FIELD  OF  NON- 
RESISTANT  COTTON.    (Photograph  by  W.  A.  Orton) 

fungus  has  been  studied  extensively  both  in  its  general  biological 
and  also  in  its  cultural  relationships,  but  it  is  not  yet  certain  that 
the  forms  on  the  different  host  plants  are  properly  referable  to  the 
same  species.  If  so,  however,  it  would  certainly  seem  that  these 
hosts  have  caused  at  least  a  racial  variation  in  the  parasite. 

Distribution.  The  wilt  disease  of  cotton  is  now  known  to  be 
one  of  the  most  destructive  parasitic  diseases  of  this  crop,  and  it 
is  probable  that  the  fungus  is  distributed  practically  throughout 


234  FUNGOUS  DISEASES  OF  PLANTS 

the  cotton-growing  states.  It  has,  however,  been  found  as  a  most 
serious  malady  in  portions  of  South  Carolina,  particularly  on  the 
sea  islands,  also  in  many  localities  of  Georgia,  Alabama,  and 
Louisiana.  It  exists  also  to  less  extent  in  other  southern  states, 
and  as  far  west  as  Arkansas.  The  writer  has  not  observed  it  in 
Texas,  although  points  in  all  parts  of  the  state  were  visited  in  1900 
and  1901.  On  the  watermelon  the  fungus  has  also  been  found 
in  much  the  same  territory,  but  most  abundant  in  Virginia  and 
South  Carolina.  The  cowpea  is  affected  in  many  southern  states. 


FIG.  97.    A  COTTON  FIELD  CONTIGUOUS  TO  THAT  IN  FIG.  96,  BUT  PLANTED 
TO  A  RESISTANT  STRAIN  OF  COTTON.    (Photograph  by  W.  A.  Orton) 

Climatic  relations.  The  wilt  diseases  do  not  appear  to  be  to 
any  great  extent  dependent  upon  climatic  conditions.  The  fungus, 
as  will  be  shown  later,  is  normally  to  be  found  in  the  soil,  where 
it  may  perhaps  exist  saprophytically  for  indefinite  periods.  Neither 
severe  temperature  changes  nor  general  differences  in  soil  condi- 
tions seem  to  be  of  special  consequence.  Plants  in  sandy  regions 
may  be  more  readily  wilted  than  those  in  soils  more  retentive  of 
moisture,  but,  at  the  same  time,  the  fungus  evidently  does  no 
greater  damage  ultimately  in  one  soil  than  in  the  other. 

Parts  of  the  plant  affected.  The  wilt  disease  of  cotton  was 
first  described  as  a  "  Frenching "  (Atkinson).  Cotton  plants  in 


ASCOMYCETES 


235 


the  heavy  soils  of  central  Alabama  were  somewhat  peculiarly 
affected  by  this  fungus.  There  is  first  a  yellowing  and  finally 
a  drying  out  of  those  portions  of  the  leaves  farthest  from  the 
main  fibro vascular  bundles,  that  is,  between  the  lobes.  Later 
such  leaves  might  fall,  or  the  whole  plant  might  become  wilted, 
and  finally  brown  and  dead.  In  other  regions  of  the  country  the 
"wilting"  is  much  more  a  characteristic  appearance,  —  the  dis- 
ease being  scarcely  noticeable,  except  in  a  stunted  condition  of 
the  plants,  until  finally  wilting  results.  In  general,  the  disease 


FIG.  98.   COTTON  PLANTS  OF  THE  SAME  AGE  :  TO  THE  LEFT,  HEALTHY  ; 
TO  THE  RIGHT,  AFFECTED  BY  WILT.    (Photograph  by  W.  A.  Orton) 

is  typically  that  of  a  wilt  in  the  case  of  both  cowpeas  and  water- 
melons. The  affected  plants  have  therefore  the  appearance  which 
any  plant  would  have  when  deprived  of  its  water  supply,  that  is, 
a  general  wilting  and  drying  up.  On  cutting  the  stem,  or  even 
the  leaf  petiole  of  affected  cotton,  a  darkening  of  the  xylem  por- 
tion of  fibrovascular  bundles  is  shown,  and  this  is  an  excellent 
indication  of  the  presence  of  this  fungus,  since  no  other  disease 
now  known  discolors  the  xylem  in  this  way.  In  some  cases 
plants  affected  and  dwarfed  show  little  or  none  of  the  characters 
in  the  stem,  yet  an  examination  of  the  larger  root  branches  and 
even  the  tap  root  would  show  the  characteristic  appearance.  In 


236 


FUNGOUS  DISEASES  OF  PLANTS 


spite  of  the  fact  that  the  disease  may  sometimes  be  suddenly 
manifested,  yet  it  is  certain  that  it  has  a  long  period  of  incuba- 
tion, and  works  very  slowly,  the  final  killing  of  the  plant  being 
effected  only  when  its  water  supply  is  almost  completely  cut  off 
by  the  filling  of  almost  all  of  the  vessels  with  the  fungous  hyphae. 
Resistance  of  the  varieties  of  the  hosts.  In  almost  any  infested 
field  it  will  be  noticed  that  there  are  plants  of  different  degrees  of 
resistance  toward  this  fungus.  In  some  plants  the  fungus  is  only 
able  to  effect  an  entrance  into  the  roots,  and  each  point  of  infec- 
tion may  be  the  point  of  origin  of  several  rootlets  developed  in 
the  form  of  a  small  tuft.  Again,  the  fungus  may  extend  practi- 
cally throughout  the  root  system  and  yet  fail  to  invade  the  stem. 
Finally,  the  whole  plant  may  sometimes  be  affected.  Two  plants 
in  the  same  hill  may  show  great  diversity  in  this  relationship. 
Therefore  it  may  be  said  that  all  degrees  of  resistance  may  be 
found.  Experiments  conducted  by  planting  many  varieties  across 
land  known  to  be  infected  by  the  disease  have  shown  interesting 
racial  variations.  Special  resistance  has  been  shown  by  some  of 
the  Egyptian  cottons,  although  they  are  not  in  any  case  wholly 
resistant.  On  the  other  hand,  sea  island  cotton  is  particularly 
susceptible  to  this  fungus.  The  most  resistant  of  the  upland  cot- 
tons thus  far  reported  are  certain  strains  of  the  variety  known  as 
Jackson,  a  limbless  sort.  The  following  interesting  table  (Orton) 
was  prepared  in  1900  : 

TABLE  SHOWING  VARIETAL  RESISTANCE  OF  COTTONS  TO  THE 
WILT  DISEASE 

(The  figures  denote  the  comparative  resistance  of  the  different  races 
on  a  scale  of  one  thousand.) 


Variety 

Resistance 

Variety 

Resistance 

<;6; 

Brady         

127 

Mitafifi  (average  of  3  strains)  . 

559 

47Q 

Cook's  Long  Staple  .    . 
Excelsior  

I24 
104 

At"l 

Drake                 .    .    . 

QO 

Sea  Island 

43J 
277 

Jones      

88 

Eldorado 

227 

King      

83 

Texas  \Vood     

162 

Peterkin    

71 

148 

Truitt     

71 

Hawkins  Prolific 

H2 

Russell  

cc 

ASCOMYCETES 


237 


In  the  same  way  as  for  the  cotton,  so  also  in  the  case  of  the 
cowpea,  resistant  races  have  been  found.  The  most  resistant  of 
the  original  varieties  tested  was  the  form  known  as  Iron  Moun- 
tain, which  has  since  been  considerably  crossed,  and  in  various 
ways  improved. 

The  fungus.  It  has  been  stated  that  this  fungus  is  unques- 
tionably very  generally  distributed  and  may  live  indefinitely  in 
the  soil.  This  is  due  to  the  fact  that  it  is  easily  propagated 
in  a  saprophytic  manner  and  may  therefore  live  in  all  probability 
a  long  period  of  time  without  the  intervention  of  the  parasitic 
habit.  The  fungus  gains  entrance  to  the  host  through  the  soil, 


FIG.  99.   NEOCOSMOSPORA  VASINFECTA.    (c  after  Erw.  F.  Smith) 
a,  the  fungus  in  xylem  of  stem ;  b  and  c,  conidial  stages  from  cultures 

and  hence  through  the  root  system.  This  is  believed  to  be  the 
sole  method  of  infection  with  the  form  on  cotton  and  cowpea. 
It  is  also  believed  that  healthy  plants  are  directly  affected  with- 
out the  assistance  of  any  other  organism  or  mechanical  effect 
causing  an  injury  through  which  the  fungus  might  obtain  access. 
The  mycelium  of  the  plant  is  at  first  found  most  abundantly  in 
the  vessels  of  the  xylem  (Fig.  99,  a) ;  but  in  later  stages  of  the 
disease  it  may  pervade  other  tissues.  Upon  the  death  of  the 
plant  it  comes  to  the  surface  along  the  lines  of  least  resistance ; 
hence  it  appears  lineally  distributed  in  the  areas  between  the 
vertical  -  lines  of  bast.  The  fungous  hyphae  are,  as  they  occur 
in  the  host  plant,  yellowish  in  color,  considerably  septate,  and 
irregularly  branched.  According  to  Atkinson  conidia  may  be 


238 


FUNGOUS  DISEASES  OF  PLANTS 


formed  within  the  vessels.  These  conidia,  frequently  spoken 
of  as  microconidia,  are  at  first  cylindrical  or  elliptical,  and  with- 
out septa ;  but  they  may  become  slightly  curved  and  once  or 
twice  septate.  These  are  capable  of  germination  and  growth 
within  the  tissues.  On  the  surface  of  the  host  and  in  culture 
a  -type  of  conidia  known  as  macroconidia  may  be  produced  in 
quantity.  These  are  lunulate  or  crescent-shaped  and  from  three 
to  five  times  septate,  measuring  30—50  x  4— 6/<i  (Fig.  99,  c).  Upon 

the  host  the  coriidio- 
phores  arise  in  loose 
stromatic  tufts  known 
as  sporodochia.  In  cul- 
ture all  gradations  be- 
tween the  small  and 
large  conidia  may  be 
observed.  Moreover,  an 
oidium-like  stage  is 

FIG.  ioo.  PERITHECIA,  Ascus,  \ND     sometimes    produced, 

and  in  the  race  of  this 
fungus    on    the    melon 
chlamydospores  are  not  uncommon  in  old  cultures. 

The  ascus  stage  of  the  fungus  has  been  found  both 
on  the  host  plant  and  in  cultures  upon  steamed  potato 
cylinders  and  other  solid  media  in  which  ascospores  were 
sown.  In  the  case  of  the  cowpea  fungus  the  line  of 
culture  work  so  accurately  followed  out  (Smith)  has 
shown  conclusively  that  the  perithecia  may  be  devel- 
oped from  both  types  of  conidia  and  that  the  perithe- 
cium  is  undoubtedly  a  stage  in  the  development  of  the  wilt 
fungus.  As  the  fungus  shows  considerable  differences  on  the 
different  hosts  in  regard  to  the  ability  to  produce  perithecia,  so 
it  shows  also  a  difference  in  the  ease  or  difficulty  with  which  the 
ascus  stage  may  be  produced  in  artificial  cultures  from  the  conid- 
ial  stage.  The  perithecium  of  the  fungus  is  superficial,  more 
or  less  scattered,  flask-shaped  (Fig.  ioo),  and  frequently  orange 
vermilion  in  color,  measuring  about  250-350  x  200-300/1,.  The 
neck  may  .be  straight  or  slightly  curved.  The  ostiolum  is  closed 
until  a  late  period  with  well-differentiated  cells,  and  within  the 


PARAPHYSIS  OF  NEOCOSMOSPORA 
b  (After  Erw.  F.  Smith) 


ASCOMYCETES  239 

neck  is  lined  with  periphyses.  The  perithecia  are  seated  upon 
a  slight  subiculum. 

The  wall  of  the  perithecium  at  maturity  is  made  up  of  paren- 
chymatous  cells  more  or  less  polyhedral  in  form.  The  asci  are 
cylindrical  in  the  spore-bearing  portion  and  measure  often  100- 
I3OX  n-14//,.  Each  ascus  contains  eight  spherical  ascospores, 
the  latter  are  brown  in  color  and  show  at  maturity  a  wrinkled 
exospore  or  surface.  Paraphyses  of  somewhat  peculiar  form  arc 
present.  These  consist  of  a  loose  chain  of  large  cells,  as  shown 
in  Fig.  100,  b.  The  development  of  the  perithecium,  apparently, 
has  not  been  studied  in  detail. 

Control.  It  is  believed  that  it  will  not  be  possible  to  control 
such  wilt  diseases  by  the  use  of  any  toxic  substances  in  the  soil. 
Prevention  is  therefore  dependent  upon  the  choice  or  develop- 
ment of  varieties  which  may  be  more  or  less  resistant  to  this 
fungus,  as  already  suggested.  Moreover,  it  will  probably  be  neces- 
sary to  look  toward  the  selection  of  varieties  locally  resistant,  since 
the  relation  of  such  varieties  to  climatic  and  soil  conditions  seems 
unquestionably  to  affect  resistance  to  this  fungus. 

Other  wilt  diseases.  Wilt  diseases  of  various  other  plants  have 
been  studied  and  some  have  been  referred  provisionally  to  the  spe- 
cies of  fungus  above  described,  such  diseases,  for  instance,  as  the 
stem  disease  of  ginseng,  the  wilt  of  the  flax,  wilt  of  okra,  etc.  There 
are,  moreover,  other  fungous  diseases  due  to  species  of  Fusarium 
which  may  or  may  not  be  conidial  stages  of  some  species  of  Neo- 
cosmospora.  Examples  of  such  diseases  are  to  be  found  in  the  stem 
blight  and  dry  rot  of  potatoes,  caused  by  Fusarium  oxysporum. 

XXXIII.    A  CANKER  OF  WOODY  PLANTS 
Nectria  cinnabarina  (Tode)  Fr. 

DURAXD,  E.  J.    A  Disease  of  Currant  Canes.    Cornell  Univ.  Agl.  Exp.  Sta. 

125:   23-38.  figs.  1-16.    1897. 
MAYR,  H.    Ueber  den   Parasitismus  von  Nectria  cinnabarina.    Unters.  a.  d. 

forst-bot.    Institut  zu  Miinchen  3:   1-16.  pi.  i.    1883. 
WEHMER,  C.   Zum  Parasitismus  von  Nectria  cinnabarina  Fr.  Zeitsch.  f.  Pflan- 

zenkr.  4:   74-84;   Ibid.    5:   268-276.  pi.  2.    1894. 

Several  important  fungous  diseases  are  attributed  to  different 
species  of  the  genus  Nectria.  Perhaps  the  two  most  destructive 


240 


FUNGOUS  DISEASES  OF  PLANTS 


of  these  Nectrias  are  Nectria  cinnabarina  (Tode)  Fr.  and  Nectria 
ditissima  Tul.  Both  of  these  fungi  seem  to  follow  other  injuries, 
but  either  may,  after  gaining  a  foothold,  spread  rapidly  from  plant 
to  plant  and  be  of  the  nature  of  an  epidemic. 

Distribution.  Nectria  cinnabarina  is  very 
commonly  distributed  throughout  temperate 
regions,  at  least,  and  may  be  found  growing 
upon  a  great  variety  of  hosts.  It  has  been  de- 
scribed as  the  probable  cause  of  an  occasion- 
ally destructive  disease  of  currant  canes,  and 
in  the  same  state  it  unquestionably  exists  as 
a  parasite  upon  the  pear.  The  horse-chestnut, 
the  china  berry,  and  other  trees  in  various  parts 
of  the  country  frequently  show  the  effects  of 
its  injuries.  Durand  submits  evidence  to  the 
effect  that  it  is  a  more  or  less  destructive  dis- 
ease to  currants  throughout  New  York,1  and 
it  has  been  mentioned  as  a  currant  disease  in 
other  sections  of  the  country,  causing  affected 
parts  to  dry  up  and  eventually  die.  In  Europe 
it  is  also  known  to  cause  disease  in  several 
hosts,  all  deciduous  trees. 

The  fungus.  The  disease  seems  to  infest 
particularly  the  cambium  and  soft  bast.  It  is 
therefore  unlike  its  relative  Neocosmospora, 
and  would  seem  to  be  more  or  less  localized, 
gaining  entrance,  as  previously  stated,  through 
wound  areas,  and  probably  killing  the  twig  or 
cane  so  soon  as  the  latter  is  girdled.  The 
hyphae  are  closely  septate,  and  large  stromatic 
areas  are  produced  upon  the  epidermis  or  within  the  cortex 
(Fig.  102).  These  rupture  the  surface  layer  and  appear  as  tuber- 
culiform  stromata,  crowned  with  minute,  short,  erect,  or  flexuous 
conidiophores  which  bear  simple,  ovate  conidia.  The  general 
appearance  of  this  stroma  superficially  is  that  of  a  pinkish  disk. 
The  conidial  stage  appears  usually  during  the  summer,  and  it  is 


FIG.  101.  NECTRIA  ON 
CURRANT.  (Photo- 
graph by  E.  J.  Durand) 


1  This  fungus  is  certainly  not  responsible  for  the  common  currant  cane  disease 
of  eastern  New  York.    The  latter,  which  is  typically  a  wilt,  is  discussed  later. 


ASCOMYCETES 


241 


generally  followed  later  in  the  season  by  the  development  of  peri- 
thecia,  which  latter  may  be  differentiated  in  newly  developed 
stroma,  or  in  the  stroma  which  has  borne  the  Tubercularia  stage.  A 
longitudinal  section  of  the  perithecia  in  a  related  fungus  is  shown 
in  Fig.  103.  The  wall  of  the  perithecium  consists  of  an  interwoven 
layer  of  threads  having  almost  a  pseudoparenchymatous  appearance. 
The  asci  develop  from  the  base  and  sides,  converging  toward  the 
apex,  each  ascus  being  club-shaped,  measuring  60-90  x  8-12/1,  and 


FIG.  102.   NECTRIA  CINNABARINA,  SECTION  OF  SPORODOCHIUM, 
WITH  YOUNG  PERITHECIUM.    (Photograph  by  E.  J.  Durand) 

containing  eight  elliptical  spores,  which  at  maturity  become  two- 
celled  by  a  partition  which  may  divide  the  spore  into  two  some- 
what unequal  parts.  The  spores  are  about  14-16  x  5 -/At. 

In  artificial  culture  the  mycelium  develops  rapidly,  and  usually 
upon  almost  any  of  the  nutrient  media.  Upon  canes,  stems,  or 
other  solid  media  the  tuberculiform  stroma  is  readily  produced. 
Both  conidia  and  ascospores  germinate  readily.  In  such  cultures 
conidia  are  produced  irregularly  upon  small  branches  of  the 
hyphae  and  sometimes  abscised  more  or  less  directly  from  large 


242  FUNGOUS  DISEASES  OF  PLANTS 

hyphae  as  yeast-like  conidial  cells.  The  cushion-like  masses  "also 
produce  conidia  in  quantity.  Mayr  described  certain  macroconidia 
borne  upon  small,  white  stromata  preceding  the  usual  cushions  on 
the  canes ;  but  Durand  was  unable  to  detect  such  spores. 


FIG.  103.   PLEONECTRIA  BEROLINENSIS:  A  CLUSTER  OF  PERITHECIA 
(Photograph  by  E.  J.  Durand) 

Control.  It  would  seem  that  the  most  practical  method  of 
control  consists  in  eradicating  diseased  vines  as  they  appear  in 
the  spring,  the  habit  and  color  of  the  affected  canes  giving  the 
necessary  clue  to  their  presence. 

XXXIV.    EUROPEAN   APPLE   CANKER 

Nectria  ditissima  Tul. 

HARTIG,  R.    Der  Krebspilz  der  Laubholzbaume,  Nectria  ditissima  Tul.    Un- 
ters.  a.  d.  forstbotan.  Institut  Miinchen  1 :    109-128.  pi.  6.    1880. 

This  disease  is  apparently  widespread  in  Europe  upon  the 
apple,  and  it  is  not  uncommon  in  the  northeastern  United  States 
upon  the  same  host.  It  may  also  appear  on  the  pear.  The  fungus 
seems  to  gain  entrance  to  the  host  through  wounds,  especially 
hailstone  bruises.  The  mycelium  penetrates  the  bark  chiefly,  but 


ASCOMYCETES  243 

to  some  extent  the  cambium  and  the  young  wood.  Much  of  the 
injured  bark  peels  off,  and  as  the  mycelium  is  perennial,  extending 
further  each  season,  large  cankers  may  be  produced. 

Unicellular  microconidia  generally  appear  first.  These  are  fol- 
lowed, usually  on  areas  killed  the  previous  season,  by  pale  stro- 
matic  cushions  of  fertile  hyphae  producing  macroconidia.  The 
latter  are  twice  or  more  septate,  sickle-shaped,  and  are  apparently 
most  important  in  the  distribution  of  the  fungus  during  the 
summer.  The  perithecia  develop  late  in  the  season,  or  the  fol- 
lowing spring,  arising  in  clusters  on  the  stromata. 

Control.  The  fact  that  this  fungus  seems  to  follow  other  injuries 
suggests  that  prevention  (where  preventive  measures  are  necessary), 
especially  in  the  case  of  susceptible  plants,  may  be  practiced  by 
simply  covering  up  the  wounds  with  a  thorough  application  of 
Bordeaux  mixture  or  white  paint.  For  example,  immediately  after 
a  hail  storm  or  after  pruning  it  might  be  desirable  to  use  the 
measures  indicated. 

XXXV.    STEM   ROT  OF  SWEET  POTATO   AND   EGGPLANT 
Nectria  Ipomaxz  Hals. 

HALSTED,  B.  D.    The  Egg  Plant  Stem  Rot.    N.  J.  Agl.  Exp.  Sta.  Rept.  12 : 
281-283.    1891. 

This  fungus  has  been  described  as  the  cause  of  the  stem  rot 
of  the  sweet  potato  (Ipomcea  Batatas}.  It  is  also  considered  to 
be  responsible  for  a  disease  marked  by  the  poor  development  and 
unfruitfulness  in  eggplant  in  New  Jersey.  The  affected  plants 
manifest  the  presence  of  the  fungus  by  a  general  unhealthfulness, 
finally  yellowing  and  wilting.  An  examination  of  the  living  plants 
may  disclose  a  creamy  white  mycelium  near  the  base  of  the  stem. 
This  mycelium,  according  to  Halsted,  bears  spores  typical  of  the 
form  genus  Fusarium,  or  the  macroconidia  of  other  species  of 
Nectria,  that  is,  curved,  hyaline,  and  pluriseptate.  Later  the  peri- 
thecial  stage  appears  in  clusters  at  the  base  of  the  stem.  Genetic 
connection  between  these  spore  forms  has  been  verified  by  arti- 
ficial cultures  and  by  cross  inoculation.  A  comparative  study  of 
the  spore  forms  indicates  that  the  disease  upon  sweet  potato  and 
eggplant  is  produced  by  the  same  fungus, 


244 


FUNGOUS  DISEASES  OF  PLANTS 


XXXVI.    ERGOT 

Claviceps  purpurea  (Fr.)  TuL 

DE  BARY,  A.    Comp.  Morphology  and  Biology  of  the  Fungi,  Mycetozoa  and 

Bacteria,  I.e.,  pp.  35-39,  220-221,  227-228. 
FISCH,    C.    Zur   Entwickelungsgesch.   einiger  Ascomyceten.    Bot.   Zeitg.  40: 

851-870,  875-897,  899-906.  pis.  /o-//.    1882. 
HEALD,  F.  D.,  and  PETERS,  A.  T.   Ergot  and  Ergotism.    Neb.  Agl.  Exp.  Sta. 

Press  Built.  23  :    1-7.    1906. 
SALMON,  D.  E.    Enzootics  of  Ergotism.     U.  S.    Dept.  Agl.  Kept.  (1884): 

212-252.  pis.  5-8. 
STAGER,  R.    Infectionsversuche  mit  Gramineen-bewohnenden  Claviceps-arten. 

Bot.  zeit.  61 :   111-158.    1903. 
TULASNE,  L.  R.    Me"moire  sur  1'Ergot  des  Glumace'es.    Ann.  d.  Sci.  Nat.  20 

(S<Sr.  3):  5-56.  pis.  1-4.    1853. 

The  ergot-producing  fungus  is  of  more  or  less 
common  occurrence  as  a  disease  of  rye  and  other 
grasses.  It  has  never  proved  a  pest  of  any  seri- 
ous importance  so  far  as  its  effects  upon  the 
host  plant  are  concerned,  but  it  deserves  special 
consideration  from  the  interesting  morphological 
characters  of  the  fungus  as  well  as  from  the  na- 
ture and  importance  of  the  officinal  and  toxic 
extract,  commonly  known  as  ergotine,  which  may 
be  obtained  from  a  certain  stage  of  the  fungus. 
The  ergot  grains  may  be  accidentally  eaten  by 
cattle  or  horses,  and  no  great  amount  is  required 
to  cause  dangerous  poisoning  or  uterine  con- 
traction, paralysis,  etc.  The  fungus  is  widely 
distributed  throughout  the  United  States  and 
Europe,  and  it  has  been  known  botanically  more 
than  half  a  century.  It  is  probably  considerably 
affected  by  climatic  or  seasonal  conditions,  since, 
as  will  be  seen,  it  must  effect  an  entrance  to  the 
host  plant  at  a  particular  time,  and  the  spores 
must  therefore  be  produced  in  abundance  in 
advance  of  this  period.  The  principal  grasses 
affected  by  the  species  here  discussed  are  Secale 
cere  ale  (rye),  Lolium  perenne  (rye  grass),  Gly- 

ceria  nervata,  Elymus  virginicus,  and  other  grasses  of  more  or 

less  economic  importance, 


FIG.  104.   ERGOT 
OF  RYE 


ASCOMYCETES  245 

The  fungus.  The  fungus  shows  an  interesting  polymorphism, 
first  producing  a  conidial  stage  upon  the  ovule  sac,  later  the 
sclerotial  or  true  ergot  stage  in  place  of  the  grain,  and  finally 
completing  its  life  cycle  by  developing  special  sporophores  from 
this  sclerotium  after  a  long  period  of  rest  has  been  undergone. 
The  fungus  is  supposed  to  gain  entrance  to  the  host  at  the  base 
of  the  ovule  sac  or  carpel,  penetrating  the  latter  and  developing 
through  it  or  over  it  as  a  hyphal  weft,  or  primary  mycelium,  the 
whole  structure  maintaining  the  general  shape  of  the  ovule  sac, 
which  is  gradually  replaced  by  the  fungous  body.  The  surface 
mycelial  areas  are  thrown  into  folds  and  numerous  short  conidio- 
phores  arise,  bearing  small  ovate  conidia.  This  is  known  as  the 
sphacelial  stage.  Insects  are  attracted  to  it  by  a  secretion,  and 
the  spores  are  by  this  means 
and  by  the  wind  effectively 
disseminated.  Meanwhile,  a 
dense  growth  of  the  fungus 
makes  its  appearance  at  the 
base  of  the  affected  part  and 
gradually  enlarges  as  a  firm, 
compact  body,  or  sclerotium. 

It  gradually  replaces  the  area    FlG"  I05"  CLancv*  ,0*****:  SCLERO- 

J  TIUM  .WITH  STROMATA 

occupied   by   the    sphacelial 

stage,  becomes  purplish  in  color,  and  in  time  projects  beyond  the 
usual  dimensions  of  the  normal  ovule  sac,  pushing  forward  upon 
its  tip  the  remnant  of  the  sphacelial  stage  and  any  portions  of  style 
and  stigma  which  may  remain.  The  sphacelial  stage  and  the  rem- 
nants of  the  ovule  sac  are  finally  brushed  away  or  fall  off  and  the 
mature  sclerotium  is  in  the  form  of  a  very  hard,  purplish  or  brown, 
slightly  curved  or  horn-shaped  body,  which  may  attain  a  length  of 
from  one  half  to  one  and  one-half  inches  (Fig.  105).  The  develop- 
ment of  this  sclerotial  stage  requires  about  the  same  length  of  time 
as  is  needed  for  the  development  of  the  grain  in  the  normal  ovule 
sacs.  It  is  therefore  mature  at  the  time  that  the  grain  is  mature. 

The  sclerotium  readily  falls  from  its  place  of  production  and 
must  then  undergo  a  long  period  of  rest  before  it  is  in  condi- 
tion to  be  brought  to  germination.  In  this  particular  species  ger- 
mination in  nature  apparently  results  early  the  following  spring. 


246 


FUNGOUS  DISEASES  OF  PLANTS 


Germination  really  consists  in  absorption  of  water,  increase  in 
size  of  the  sclerotial  mass,  and  the  pushing  into  growth,  some- 
times from  many  different  points  on  the  sclerotium,  of  compact 
masses  of  hyphse,  which  develop  into  sporo- 
phores.  These  sporophores  may  be  from  one 
fourth  to  one  inch  in  height,  and  they  bear  at 
the  summit  head-shaped  stromata  within  which 
the  perithecia  are  differentiated.  A  cross  sec- 
tion of  the  head-shaped  stroma  is  shown  in 
Fig.  1 06,  a. 

The  sporophorc  consists  of  a  stalk  from  one 
half  to  one  inch  in  length,  terminated  by  a 
capitate  enlargement  about  twice  the  diameter 
of  the  stalk  portion.  In  the  stromatic  tissue  of 


FIG.  106.    CLAVICEPS  PURPUREA  :  SECTION  OF  STROMA  AND  ENLARGED 
PERITHECIUM  ;  ALSO  ASCI  AND  SPORES.    (After  Tulasne) 

the  head  numerous  perithecia  are  formed  near  the  periphery.  So 
far  as  is  known,  a  perithecium  is  developed  in  two  successive 
stages  :  (i)  By  the  repeated  division  of  a  few  differentiated  cells 
below  the  surface  there  results  an  ellipsoidal  pre-ascal  tissue.  (2)  In 
the  proximal  or  basal  portion  of  this  cellular  body  an  hymenium 


ASCOMYCETES 


247 


originates,  and  the  asci  to  which  it  gives  rise  obtain  room  for  com- 
plete development  either  by  forcing  the  separation  of  the  cells  in 
the  center  of  the  cellular  body  or  by  dissolving  some  of  these.  The 
mature  perithecium  consists  of  a  flask-shaped  structure,  the  mouth 
of  which  projects,  along  with  the  tissues  which  inclose  it,  slightly 
beyond  the  general  level  (Fig.  106,  b).  Within  the  neck  of  this 
perithecium  are  to  be  found  many  periphy- 
ses.  The  mature  asci  are  long-clavate.  Each 
ascus  contains  eight  filiform  spores,  averaging 
60—70 /A  in  length,  which  issue  from  the  tip 
of  the  ascus  and  readily  germinate  in  water 
(Fig.  1 06,  c). 

Control.  Proper  precautions  in  the  selec- 
tion of  the  grain  seed,  together  with  thorough 
preparation  of  the  land,  obviate  any  danger  in 
the  case  of  rye.  When  detected  in  the  har- 
vested product,  the  sclerotia  must  be  shaken 
out  or  the  product  discarded.  When  ergot 
appears  in  abundance  on  grasses  in  the  pas- 
ture, either  the  animals  must  be  taken  off 
until  the  ergot  falls,  or,  where  possible,  the 
grass  may  be  mowed  with  a  machine  the  blade 
of  which  may  be  set  high.  In  the  latter  case 
subsequent  raking  may  be  unnecessary.  In 
the  central  West,  ergot  is  not  uncommon  on 
the  chief  pasture  crop,  blue  grass  (Poa  pratensis}.  This  may  not 
be  ergot  of  rye,  for  besides  that  species,  two  ergot-producing  fungi 
have  been  reported  on  Poa,  Claviceps  microcephala  (Wallr.)  Tul. 
and  Claviceps  setulosa  (Quel.)  Sacc.1 

1  A  disease  of  rice  known  as  green  smut  is  well  developed  in  the  rice-growing 
regions  of  Japan  and  Louisiana.  The  effect  of  the  fungus  is  conspicuous  (Fig.  107), 
although  only  a  few  grains  in  a  head  are  affected.  The  disease  has  every  appear- 
ance externally  of  being  a  smut.  Brefeld  (Unters.  a.  d.  Gesammtg.  d.  Myk.  12  : 
194)  and  others  have  studied  this  form.  Brefeld  has  studied  also  more  particularly 
a  related  species  on  Setaria  crus-ardea.  In  both  cases  the  smut-like  body  is  a 
typical  sclerotium  surrounded  by  looser  hyphae  and  the  dark  walled  spores.  Germi- 
nation studies  of  the  spores  seem  to  indicate  that  they  are  conidia,  and  it  has 
been  suggested  that  the  fungus  may  prove  to  be  an  ascomycetous  form,  possibly 
one  of  the  Hypocreales.  The  species  on  rice  bears  the  name  Ustilaginoidea  Oryzce 
(Cke.)  Tak. 


FIG.  107.  USTILAGINOI- 
DEA ON  RICE.  (Photo- 
graph by  H.  R.  Fulton) 


248  FUNGOUS  DISEASES  OF  PLANTS 

XXXVII.  DOTHIDIACE^: 

This  family  includes  several  hundred  species,  very  few  of  which, 
however,  are  of  great  importance  as  disease-producing  parasites. 
It  is  characterized  by  asci  arising,  apparently,  for  the  most  part, 
directly  from  the  stromatic  tissue,  or  at  least  by  a  very  indistinct 
perithecium,  or  perithecial  wall.  They  differ  from  the  Hypocreaceae 
especially  in  the  color  of  the  stroma,  which  is  dark  to  black.  The 
most  important  species,  Plowrightia  morbosa,  black  knot  of  the 
plum,  is  discussed  at  length,  but  the  genus  Phyllachora  is  important 
from  the  number  of  its  species  and  the  variety  of  its  hosts. 

XXXVIII.    BLACK  KNOT  OF  PLUMS  AND  CHERRIES 
Ptowrightia  morbosa  (Schw.)  Sacc. 

BEACH,  S.  A.    Black  Knot  of  Plum  and  Cherry.    N.  Y.  Agl.  Exp.  Sta.  Built. 

40:   25-34.    1892. 
FARLOW,  W.  G.  The  Black  Knot.  Bussey  Institution,  Built.  (1876):  440-453. 

pis.  4-6. 
HALSTED,  B.  D.    Destroy  the  Black  Knot  of  Plum  and  Cherry  Trees.    N.  J. 

Agl.  Exp.  Sta.  Built.  78  :    1-14.    1891. 
HUMPHREY,  J.  E.  The  Black  Knot  of  the  Plum.    Mass.  Agl.  Exp.  Sta.  Rept. 

8:   200-210.  pi.  i.    1890. 
LODEMAN,  E.  G.    Black  Knot.   Cornell  Univ.  Agl.  Exp.  Sta.  Built  81 :  637- 

657.    1894. 

This  is  one  of  the  most  common  and  most  striking  fungous 
diseases  of  fruit  trees  in  the  United  States.  It  has  been  known 
and  described  in  orchard  literature  since  the  early  part  of  the  nine- 
teenth century,  and  the  causal  fungus  was  described  by  Schweinitz 
in  1822.  For  a  long  time,  however,  the  knot  was  commonly 
supposed  to  be  caused  primarily  by  insects.  A  considerable  litera- 
ture upon  this  disease  accumulated,  but  it  was  not  until  1876  that 
a  thoroughly  competent  account  of  the  fungus  and  its  relation  to 
the  knot  was  presented.  This  latter  account  has  remained  the 
chief  basis  of  opinions  concerning  this  fungus. 

Geographical.  The  black  knot  was  apparently  at  one  time  con- 
fined largely  to  the  Atlantic  seaboard,  and  was  particularly  abundant 
only  in  New  England  and  perhaps  New  York.  It  is  now  known 
to  extend  across  the  northern  United  States  to  the  Pacific  Coast, 
although  very  large  portions  of  the  Southwest  and  large  areas  of 


ASCOMYCETES  249 

the  central  West  are  practically  free  from  this  disease.  In  spite  of 
the  interchange  of  plants  between  Europe  and  America,  the  black 
knot  has  not  yet  been  reported  from  either  England  or  from  the 
continent,  and  so  far  as  can  be  ascertained,  it  is  not  known  to 
occur  in  other  countries. 

Host  plants.  Very  few  of  the  native  species  of  plum  or  cherry 
are  free  from  this  fungus.  Among  those  which  suffer  particularly 
from  the  disease  may  be  mentioned  the  Chickasaw  plum  (Primus 
aiignstifolia\  the  yellow  plum  (Primus  americana),  the  wild  black 
and  red  cherries  (Primus  serotina  and  Primus  pennsylvanicd), 
chokecherry  (Primus  virginiana\  the  bird  cherry  (Primus  avium), 
and  the  morello  varieties  (Primus  Cerasus).  It  is  said  to  occur 
upon  other  species,  but  definite  records  are  not  at  hand.  On  ac- 
count of  the  fact  that  this  fungus  attacks  wild  plums  as  well  as 
cultivated,  it  is  a  constant  source  of  danger  to  plum  growing  wher- 
ever the  native  plums  abound  in  neglected  places.  In  certain 
seasons  the  knot  will  be  found  in  abundance  upon  some  species 
only,  while  it  will  almost  entirely  omit  other  hosts.  This  has 
prompted  the  opinion  that  there  may  be  several  species  or  forms 
of  the  fungus  affecting  the  different  hosts.  This  may  be  true,  but 
it  would  appear  to  be  almost  as  well  explained  by  admitting  the 
very  evident  fact  that  certain  hosts  are  in  general  more  susceptible 
and  by  assuming  that  during  some  seasons  particular  species  may 
be  rendered  peculiarly  susceptible. 

Symptoms.  The  black  knot  is  a  most  unsightly  disease,  con- 
sisting of  wart-like  hypertrophies  or  excrescences  which  may  cover 
a  considerable  area  on  the  twigs  and  limbs.  It  is  confined  entirely 
to  the  woody  parts.  The  term  black  knot  applied  to  this  disease 
is  a  very  fortunate  one,  since  the  deformities  take  the  form  of 
elongated  blackened  knots,  usually  extending  a  distance  of  from 
one  or  two  to  four  or  five  inches  upon  the  affected  branches. 
For  the  .most  part  the  injury  is  confined  to  one  side  of  the 
branch,  or  at  least  it  does  not  generally  form  a  complete  ring, 
which  would  effectually  cut  off  the  nutriment  from  the  tip  portion. 
The  first  appearance  of  the  knot  is  usually  noted  in  the  spring, 
although  it  has  also  been  observed  to  make  its  appearance  in  the 
fall  (Humphrey).  At  first  it  consists  of  a  slight  swelling  of  the 
branch,  originating  upon  any  portion  whatever,  but  generally  on 


25° 


FUNGOUS   DISEASES   OF  PLANTS 


that  portion  of  a  limb  bearing  a  side  branch.  It  may  arise  inde- 
pendently, or  near  an  old  knot.  As  the  swelling  increases  in  size 
the  bark  is  broken  and  the  stroma  of  the  fungus  then  becomes 


FIG.  1 08.    PLOWRIGHTIA  MORBOSA,  BLACK  KNOT  OF  PLUM.    (After  Longyear) 

evident.  By  midsummer  the  knot  will  have  attained  full  size,  and 
from  that  time  until  the  winter,  or  as  long  as  the  remnants  of  the 
knot  may  persist,  it  will  be  deep  black  and  carbonaceous  in  tex- 
ture (Fig.  1 08,  a).  In  the  case  of  small  twigs  which  are  affected, 
bending  may  be  caused,  so  that  a  right  angle  will  be  made  from 


ASCOMYCETES  251 

the  knotted  side.  While  the  smaller  twigs  are  usually  affected, 
the  knot  may  also  be  found  upon  branches  nearly  two  inches  in 
diameter. 

The  fungus.  The  mycelium  of  the  fungus  is  found  during  the 
early  stages  occupying  most  of  the  cambium  and  the  bast  areas, 
as  well  as  extending  throughout  the  cortex.  If  the  whole  cambium 
ring  becomes  affected  the  girdling  causes  the  death  of  the  limb  be- 
yond. In  general,  however,  the  growth  of  the  twig  continues,  since 
the  fungus  is  confined  to  one  portion  of  the  cambium,  growing 
from  this  layer  towards  the  periphery.  The  knot  itself  is  made 
up  of  a  mass  of  tissue,  comprising,  on  the  one  hand,  dense  areas 
of  the  fungus  and,  on  the  other,  various  cells  or  tissue  elements  of 
'the  host.  Bast  fibers,  parenchyma  cells,  and  even  vessels  may  be 
found  in  this  heterogeneous  mass  in  which  all  of  the  associations 
of  cells  normally  present  have  disappeared.  This  abnormal  con- 
dition is  apparently  brought  about  by  the  breaking  up  of  the 
cambium  and  a  resulting  development  of  all  the  various  cell  forms 
to  which  it  may  give  rise  in  the  diverse  isolated  areas.  The  dis- 
tribution of  the  fungous  hyphae  and  the  miaute  anatomy  of  the 
knot  varies  upon  different  hosts. 

During  the  development  of  the  knot  in  the  spring,  small, 
greenish  areas  may  be  noticed  upon  the  surface,  and  later  the 
mycelium  breaks  through  the  bark  from  all  directions  and  forms 
upon  the  surface  a  very  dense  layer  of  closely  adherent  or  pseudo- 
parenchymatous  cells.  This  stromatic  fungous  layer  gives  rise  to 
conidiophores,  which  are  flexuous  and  septate  (Fig.  108,  c).  Each 
conidiophore  produces  a  spore  at  the  tip,  and  by  further  growth 
scars,  geniculations,  or  short  branches  may  result.  The  conidio- 
phores are  produced  in  such  quantity  that  the  surface  has  a  vel- 
vety appearance  ;  they  measure  from  40-60  x  4-5  p.  The  conidia 
are  simple,  and  light  brown  in  color.  The  period  of  conidial 
production  usually  extends  from  late  spring  until  midsummer. 
Gradually,  as  the  season  advances,  the  velvety  surface  disappears, 
disclosing  a  deep  black  stroma  which  has  been  gradually  differ- 
entiated. From  an  early  period  there  can  be  observed  with  a 
hand  lens  certain  papillae  which  locate  the  forming  perithecia 
in  this  stromatic  area.  The  later  conidiophores  are  therefore 
still  evident  on  the  surface  when  developing  perithecia  are  easily 


252  FUNGOUS  DISEASES  OF  PLANTS 

demonstrated  through  sections.  The  perithecium  contains  at  ma- 
turity the  ascospores,  or  perfect  stage,  of  this  fungus.  Owing  to 
the  dense  structure  of  the  knot,  it  is  almost  impossible  to  follow 
closely  the  stages  of  development  in  the  hymenial  tissue  and  in 
the  formation  of  the  asci.  The  asci,  at  any  rate,  develop  during 
the  winter,  and  the  spores  are  ripe  during  midwinter  or  later,  de- 
pending upon  the  region.  Each  mature  ascus  is  about  120  /u  in 
length,  and  contains  eight  spores,  the  spores  being  two-celled  by 
a  cross  wall  which  separates  unequal  portions.  They  may  be  vari- 
ously arranged  in  the  ascus  but  are  often  obliquely  uniseriate,  each 
being  16-20  x  8-io/i.  Paraphyses  are  always  present.  These  are 
filiform,  nonseptate  structures  with  a  slightly  enlarged  tip.  Other 
spore  stages,  a  stylosporic  and  a  pycnidial  stage,  have  been  found 
associated  with  the  two  already  described,  but  they  are  not  of  com- 
mon occurrence,  and  may  not  represent  fixed  and  common  stages 
in  the  life  history  of  this  species. 

The  conidia  and  the  ascospores  germinate  in  plum  juice  or 
upon  various  nutrient  media,  and  pure  cultures  may  be  readily 
made  upon  solid  media.  The  spores  also  germinate  in  water. 
Humphrey  succeeded  in  developing  a  pycnidial  form  upon  nutri- 
ent gelatin  which  differed  from  any  stage  of  the  fungus  found 
on  its  natural  hosts. 

In  spite  of  the  good  work  which  has  been  done  upon  the  de- 
velopment of  this  fungus,  there  is  opportunity  for  much  more 
careful  morphological  study.  It  would  be  necessary  to  study  the 
plant  upon  different  hosts  and  upon  various  culture  media  in  pure 
cultures  in  order  to  determine  the  ultimate  relationships  of  the 
different  spore  forms  which  have  thus  far  been  described. 

Control.  It  is  evident  that  since  the  conidial  stage  is  produced 
abundantly  during  late  spring  and  early  summer,  pruning  out  of 
the  developing  knots  just  prior  to  the  season  mentioned  would 
largely  control  the  spread  of  this  fungus  by  the  conidial  stage. 
A  similar  careful  pruning  should  be  given  prior  to  the  develop- 
ment of  the  ascospores,  if  any  knots  have  been  overlooked.  It 
would  be  well,  however,  to  make  several  prunings  during  the  year 
if  this  method  of  eradication  alone  is  practiced.  The  suppression 
of 'black  knot  has  been  a  subject  of  legislation  in  many  states,  and 
in  those  in  which  it  is  fairly  well  under  control,  pruning  is  usually 


ASCOMYCETES  253 

sufficient  to  prevent  the  spread  from  occasional  outbreaks.  Since, 
however,  wild  plums  and  cherries  everywhere  may  be  affected, 
eradication  is  difficult.  In  many  regions  the  fungus  is  so  com- 
mon and  so  persistent  that  it  is  necessary  to  take  additional  pre- 
cautions. Spraying  with  Bordeaux  mixture  has  been  advised,  and 
where  spraying  is  given,  one  application  should  be  made  during 
the  late  winter  and  one  when  the  buds  begin  to  swell.  This  latter 
should  be  followed  by  two  or  three  subsequent  applications  as  may 
seem  necessary.  It  has  been  thoroughly  demonstrated,  however, 
that  the  disease  is  controllable,  and  when  cooperation  is  given, 
eradication  in  large  areas  is  perhaps  possible. 

XXXIX.  SPHyERIALES 

The  sphaeriaceous  Ascomycetes  constitute  an  order  (sometimes 
considered  a  suborder)  containing  more  species  than  perhaps  any 
other  equivalent  natural  group  of  the  fungi.  The  great  majority 
are  saprophytic  in  habit,  occurring  upon  decaying  twigs,  leaves, 
and,  in  fact,  upon  practically  all  kinds  of  vegetable  matter,  or 
upon  the  soil.  There  are  some  notable  parasitic  species,  but 
these  are  relatively  inconsiderable  as  compared  with  the  great 
number  of  saprophytes. 

The  mycelium  may  be  light  or  dark  colored,  usually  the  latter, 
and  the  perithecia  show  very  diverse  characters  with  respect  to 
texture  and  form  of  the  ostiolum,  as  also  with  relation  to  the  sub- 
stratum and  stroma.  They  may  be  free,  slightly  connected  by  a 
scant  subiculum,  or  more  or  less  imbedded  in  a  stromatic  tissue 
of  variable  texture.  The  perithecia  vary  from  membranous  to 
carbonaceous,  delicate,  tough,  or  brittle,  and  the  ostiolum  may 
be  merely  a  circular  aperture,  a  slight  papillate  opening,  or  a 
long  beak.  What  has  been  said  of  conidial  stages  under  the 
Ascomycetes  in  general  applies  in  particular  to  this  group,  these 
stages  being  manifold,  so  far  as  the  method  of  conidiospore  pro- 
duction is  concerned. 

This  order  is  commonly  subdivided  into  eighteen  families, 
which  differ  from  one  another,  however,  in  characters  so  slight 
that  a  brief  key  of  those  which  are  here  to  be  considered  may 
be  sufficiently  descriptive. 


254  FUNGOUS  DISEASES  OF  PLANTS 

A.  No  stroma  present;  perithecia  for  the  most  part  completely  immersed 

in  the  substratum,  or  finally  becoming  more  or  less  free  by  the  rup- 
ture of  the  inclosing  matrix  (epidermis  in  the  parasitic  forms). 

1.  Perithecia  for  the  most  part  without  distinct  beak,  tough  but 

not  carbonaceous. 

a.  Asci  arising  in  groups  from  the  perithecial  wall  with- 

out intervening  paraphyses   .     MycosphcsrellacecE 
(Represented  by  Guignardia  and  Mycosph&rella^ 

b.  Asci  arising  from  the  base  of  the  perithecium  and 

not  in  groups.    Paraphyses  present.    Pleosporacea 
(Represented  by  Venturia^ 

2.  Perithecia  carbonaceous  or  tough  leathery,  as  a  rule  with 

a  distinct  beak.    Asci  thickened  at  the  apex,  commonly 

breaking  open  by  a  pore Gnomoniacece 

(Represented  by  the  genera  Glomerella  and  Gnomonia^ 

B.  No  stroma  present ;  perithecia  free  upon  the  substratum,  or  surrounded 

at  the  base  by  a  dense  mycelial  mat Sphccriacece 

(Represented  by  Rosellinia.} 

C.  Stroma  present,  consisting  of  intermixed  and  modified  fungous  and  host 

elements ;  perithecia  imbedded ;  pycnidia  present   .     .     .    Valsacece 
(Represented  by  Diaporthe.} 

D.  Stroma  present,  consisting   of  fungous  hyphse  only;    perithecia  im- 

mersed   Xylariacece 

(Represented  by  Nummularia.} 


XL.    BLACK  ROT   OF  GRAPES 
Guignardia  Bidwellii  (Ell.)  Viala  &  Ravaz 

EDSON,  A.  W.  The  Black  Rot  of  the  Grape  in  North  Carolina  and  Its  Treat- 
ment. N.  C.  Agl.  Exp.  Sta.  Built.  185  :  131-150.  1903. 

JACZEWSKI,  A.  V.  Uber  die  Pilze,  welche  die  Krankheit  der  Weinreben 
"Black  Rot"  verursachen.  Zeitsch.  f.  Pflanzenkr.  10:  257-267.  figs. 
1-8.  1900. 

REDDICK,  D.  The  Black-Rot  of  the  Grape  and  Its  Control.  Cornell  Univ. 
Agl.  Exp.  Sta.  Built.  253:  367-388.  Jigs.  177-187.  1908. 

Report  on  Experiments  made  in  1888  in  the  Treatment  of  the  Downy  Mil- 
dew and  Black  Rot  of  the  Grape  Vine.  U.  S.  Dept.  Agl.  Bot.  Div. 
Built.  10:  i -6 1.  1889. 

SCRIBNER,  F.  L.  The  Fungous  Diseases  of  the  Grape  Vine.  Bot.  Div.  U.  S. 
Dept.  Agl.  Built.  2  :  28-34.  ///.  1886. 

SCRIBNER,  F.  L.  Fungous  Diseases  of  the  Grape  and  Other  Plants  and  their 
Treatment.  1890. 

VIALA,  P.  Les  maladies  de  la  vigne.  595pp.  19 pis.  290 figs.  (Black  Rot: 
156-203.  pi.  4.  figs.  4.8-54.}  1893.  Montpellier  et  Paris. 

VIALA,  P.,  et  FERROUILLAT,  P.  Manuel  pratique  pour  le  traitement  des  mal- 
adies de  la  vigne.  1888. 


ASCOMYCETES 


255 


Distribution.  The  most  serious  menace  to  grape  growing  in 
most  sections  of  the  United  States  is  the  well-known  black  rot, 
a  fungus  of  American  origin,  the  effects  of  which  have  been 
known  for  considerably  more  than  half  a  century. 

The  black  rot  is  now  very  generally  distributed  throughout 
the  grape-growing  sections  of  the  United  States  and  is  reckoned 
with  as  a  constant  foe  wherever  susceptible  varieties  are  grown. 
It  is  supposed  to  have  been  introduced  into  France  somewhat 
more  than  twenty  years  ago,  and  it  is  now  common  in  other  sec- 
tions of  Europe,  and  throughout  the  Mediterranean  region.  Its 
ravages  are  more  serious  under  the  conditions  which  commonly 


FIG.  109.   BLACK  ROT  OF  GRAPE,  SHOWING  PROGRESS  OF  THE  DISEASE 
(Photograph  by  Donald  Reddick) 

encourage  the  growth  of  parasitic  fungi,  that  is,  moist,  warm  days, 
or  the  muggy  weather  of  midsummer,  being  particularly  favorable 
for  its  rapid  development  and  spread. 

Symptoms.  The  black  rot  fungus  occurs  upon  the  berries  and 
leaves  (Figs,  no,  in),  also  upon  fruit  pedicels,  and  sometimes 
upon  young  canes.  The  berries  are  most  severely  affected,  al- 
though the  disease  may  first  be  seen  upon  the  leaves.  Upon  the 
latter  it  appears  as  sharply  defined,  nearly  circular,  brown  spots. 
Sooner  or  later  small  pycnidia  may  be  found  at  the  centers  of 
these  spots.  The  berries  are  not  ordinarily  attacked  until  about 
two  thirds  grown.  The  first  sign  of  injury  is  the  appearance  of 
a  purplish  or  livid  brown  spot,  which  normally  spreads  over  the 
whole  surface  of  the  berry.  The  affected  fruit  gradually  becomes 


256 


FUNGOUS  DISEASES  OF  PLANTS 


darker  in  color,  and  pycnidia,  appearing  as  black  papillae,  may  be 
produced  over  the  entire  surface.  At  this  stage  the  effects  of  the 
fungus  are  therefore  unmistakable.  Later  the  fruit  shrivels  in  a 
characteristic  manner,  but  does  not,  as  a  rule,  fall  or  shell.  The 
berries  on  bunches  thus  affected  may  hang  on  the  vines  through- 
out the  season.  The  pycnidia  may  also  be  easily  observed  with 
the  unaided  eye  upon  the  dried  berries. 

Susceptibility  of  varieties.  It  seems  to  be  the  general  experi- 
ence that  practically  all  of  the  more  commonly  cultivated  varieties 

of  grapes,  particularly,  how- 
ever, the  dark  colored  va- 
rieties, including  Concord, 
Hartford,  Roger's  Hybrids, 
etc.,  are  susceptible.  In  some 
districts  certain  light  col- 
ored varieties  are  more  re- 
sistant and  the  Scuppernong 
is  practically  free  from 
attack.  In  this  case,  how- 
ever, as  in  many  others 
already  mentioned,  there  is 
a  great  difference  in  the  re- 
sistance of  varieties  accord- 
ing to  their  environmental 
conditions.  For  all  commer- 
cial purposes  grape  growing 
would  be  impossible  in  most 
localities,  on  account  of  the 
great  losses  entailed,  if  the 
disease  were  not  practically  controllable  by  spraying  operations. 

The  fungus.  The  mycelium  of  this  fungus  is  found  in  the 
outer  portions  of  affected  berries,  but  mycelium  is  never  abun- 
dant. Under  favorable  weather  conditions  only  about  one  week 
may  be  required  from  the  time  of  infection  to  the  development  of 
the  pycnidia,  —  ordinarily  8-12  days  are  necessary.  The  pycnidia 
have  long  been  known  under  the  name  Phoma  nvicola  B.  &  C. 
Upon  the  leaves  the  pycnidial  stage  has  passed  under  the  name 
Phyllosticta  Labrusca.  The  pycnidium  develops  from  a  stromatic 


FIG.  no.  GRAPES  AFFECTED  BY  BLACK  ROT 
(Photograph  by  F.  C.  Stewart) 


ASCOMYCETES 


257 


mass  of  mycelium  which  arises  beneath  the  epidermis.  It  is 
broadly  elliptical,  with  a  rather  thick  wall  and  no  indication  of  a 
beak  (Fig.  112,  a).  The  conidiophores  are  short  and  simple,  bear- 
ing spores  —  ovate  or  elliptical  —  measuring  ordinarily  8— 10  x  7— 
8 /-i.  In  moist  weather  the  spores  are  pushed  out  in  vermiform 


FIG.  in.   PHYLLOSTICTA  STAGE  OF  THE  BLACK  ROT  FUNGUS 
(Photograph  by  H.  H.  Whetzel) 

masses  and  upon  dissemination  they  are  capable  of  immediate 
germination.  Accompanying  these  pycnidia  (the  spores  of  which 
are  frequently  known  as  stylospores)  there  may  be  found  some- 
what smaller,  more  nearly  spherical  pycnidia  (commonly  but  un- 
fortunately known  as  spermagonia).  The  latter  contain  relatively 
long  filiform  conidiophores  converging  towards  the  center,  and 


258 


FUNGOUS  DISEASES  OF  PLANTS 


upon  these  are  borne  minute,  cylindrical,  or  slightly  curved 
conidia.  It  is,  however,  doubtful  if  this  last  mentioned  pycnidial 
form  is  either  common  or  of  much  consequence  in  the  rapid 
distribution  of  the  fungus. 

The  ascigerous  stage  was  first  found  and  named  in  1880,  and 
since  that  time  the  name  has  been  more  frequently  changed  than 
has  the  fungus  been  accurately  studied.  It  is  stated  that  the  asci 
were  first  found  upon  berries  which  had  hung  upon  the  vines 
during  the  winter  and  had  subsequently  been  dropped  into  water 
for  a  few  days.  Since  that  time  the  perfect  stage  (Fig.  112,  b)  has 

been  frequently  detected  on  af- 
fected berries  which  have  lain 
under  favorable  conditions  dur- 
ing the  spring  months,  as  when 
covered  by  leaves  and  grass.  It 
would  seem,  however,  that  very 
few  observations  have  been 
systematically  made  to  deter- 
mine the  time  of  development 
of  the  ascospores.  The  asci 
may  apparently  develop  in  per- 
ithecia  which  have  previously 
served  as  pycnidia,  or  resting 
stromatic  masses  may  give  rise 
to  the  perithecia  directly.  The 
asci  are  broadly  clavate,  some- 
times slightly  curved,  and  they 
contain  eight  nonseptate,  hyaline  spores,  the  latter  measuring  1 2- 
17  x  4. 5-5 /^.  They  are  generally  ovate. 

Control.  The  most  efficient  remedy  for  the  black  rot  is 
Bordeaux  mixture.  After  cleaning  the  vineyard  as  well  as  possi- 
ble of  the  pruned  and  diseased  litter,  the  old  berries  being 
covered  by  early  plowing,  Bordeaux  should  be  thoroughly  applied, 
covering  vines,  posts,  and  trellis  just  as  the  buds  are  swelling  in 
the  early  spring.  A  second  application  is  made  as  the  buds 
unfold,  and  subsequently  the  vines  should  be  sprayed  about  every 
two  weeks,  until  five  or  six  applications  have  been  made.  The 
nature  of  the  season,  however,  will  determine  how  late  it  will  be 


FlG.   112.     GuiGNARDIA   BlDWELLII:  SEC- 
TIONS  OF   PHOMA  AND  ASCIGEROUS 
STAGES 


ASCOMYCETES 


259 


necessary  to  continue  such  operations.  To  one  familiar  with  the 
life  history  of  the  fungus  it  is  evident  that  the  time  for  spraying 
will  be  governed  by  the  condition  in  which  the  fungus  is  found. 
When  no  spores  are  being  produced  spraying  may  be  unneces- 
sary ;  when  spores  are  being  produced  in  quantity  weekly  spray- 
ings may  be  demanded.  Moreover,  when  it  is  necessary  to  spray 
during  the  late  season,  ammoniacal  copper  carbonate  may  be  sub- 
stituted for  the  Bordeaux,  in  order  to  avoid  the  unattractive  dis- 
coloration of  the  fruit. 

XLI.    CRANBERRY  SCALD 
Guignardia   Vaccinii  Shear 

SHEAR,  C.  L.    Cranberry  Diseases.    Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built. 
110:    1-64.  pis.  1,2.    1907. 

Distribution  and  effects.  Under  the  name  of  scald  a  number 
of  fungi  affect  the  cranberry,  but  the  most  important  diseases  of 
this  plant  are  produced  by  the  fungus  above  mentioned.  It  has 
been  estimated  that  the  annual  loss  from  cranberry  scald  is  about 
$200,000,  and  that  this  fungus  is  responsible  for  the  greater  part 
of  this  amount.  The  disease  is  more  common  toward  the  south- 
ern limit  of  cranberry  culture,  especially  from  New  Jersey  south- 
ward, whereas  further  to  the  north,  as  in  Massachusetts,  it  is  far 
less  destructive. 

The  fungus  may  attack  very  young  fruit,  and  even  flowers, 
which  promptly  shrivel  and  die.  The  latter  effect  is  commonly 
known  as  "blast."  Upon  such  parts  the  pycnidial  stage  of  the 
fungus  is  commonly  found.  The  term  scald  is  applied  partic- 
ularly to  the  effect  upon  the  berry,  which  begins,  according  to 
Shear,  as  a  small  watery  spot  upon  the  surface  of  young  fruit. 
This  spot  may  remain  small  under  certain  conditions,  and  again 
it  spreads  quickly,  often  concentrically,  rendering  the  whole  berry 
soft,  and  sometimes  marked  by  rings.  This,  however,  is  not  a 
definite  character.  There  is  little  superficial  evidence  of  the  pres- 
ence of  the  fungus,  unless  the  berries  are  attacked  before  they  are 
half  grown,  when  they  may  promptly  shrivel  and  develop  the 
pycnidia  of  the  fungus.  The  fungus  also  affects  the  leaves,  and 
when  found  upon  these  parts,  brown  spots,  irregular  in  outline, 


260 


FUNGOUS  DISEASES  OF  PLANTS 


are    produced    within  which  areas  the  pycnidia  may  be  found. 
Cuttings  may  also  be  affected. 

The  fungus.  The  pycnidial  stage  is  a  characteristic  Phoma  or 
Phyllosticta,  100  to  120/4  in  diameter,  as  shown  in  Fig.  113. 
These  are  distributed  over  the  affected  surfaces,  and  produce 
abundant  conidia,  which  are  hyaline,  obovoidal,  frequently  trun- 
cated at  the  apex,  measuring  10.5-13.5  x  5-6/4.  The  conidia  are 
appendaged,  and  they  are  expelled  from  the  perithecium  much  as 
in  the  black  rot  of  the  grape.  The  ascogenous  form  is  less  com- 
monly found.  In  this  the  perithecia  are  much  as  those  already 
described,  except  that  the  wall  is  denser  and  they  bear  only  asci. 
The  latter  are  more  or  less  clavate,  with  a  total  length  of  from 


FIG.  113.    GUIGNARDIA  VACCINII  ON  CRANBERRY:  PYCNIDIAL  AND  ASCIGEROUS 
STAGES.    (After  Shear) 

60  to  80/4.  The  spores  are  hyaline  when  young,  and  tinted  when 
old.  They  are  described  as  elliptical  or  subrhomboidal  in  form, 
with  granular  contents  (Fig.  1 13,  £). 

This  fungus  has  been  carefully  cultivated,  cultures  being  made 
from  both  stages  and  from  hyphae,  as  well  as  from  the  tissue  of 
the  host  beneath  the  scalded  area  upon  the  berries.  It  is  reported 
to  grow  well  upon  acid  and  neutral  media,  and  especially  vigorous 
upon  corn  meal  in  various  combinations.  The  pycnidial  form  has 
been  produced  in  culture ;  yet  in  many  cultures  the  conidia  are 
not  produced  in  the  perithecia,  but  the  latter  remains  as  a  more 
or  less  sclerotial  organ.  The  ascogenous  form,  however,  has  been 
secured  in  cultures  from  both  berries  and  leaves.  After  a  few 
generations  in  culture  tubes,  the  fungus  appeared  to  lose  con- 
siderably in  vitality,  and  frequently  developed  no  spore  forms 


ASCOMYCETES  261 

after  one  or  two  generations.  In  general,  the  conditions  under 
which  growth  takes  place  do  not  seem  to  affect  to  any  great  ex- 
tent production  of  fruiting  stages.  It  is  believed  also  that  after 
the  fungus  has  penetrated  the  host  it  may  remain  under  favorable 
conditions  inactive  for  some  time,  and  that  therefore  the  period  of 
incubation  may  be  long  or  short,  depending  upon  conditions.  The 
ascogenous  form  has  not  been  found  abundantly  in  nature,  and 
may  not  be  very  important  in  the  distribution  of  the  fungus. 

Control.  Prevention  should  concern  itself  particularly  with 
sanitation,  including  the  renovation  of  the  cranberry  bog,  proper 
regulation  of  the  water  supply,  and  the  development  of  disease- 
resistant  strains.  Spraying  with  Bordeaux  mixture  has  also  proved 
of  value.  In  spraying,  however,  the  addition  of  substances  ren- 
dering the  mixture  more  adhesive  is  necessary. 

XLII.    LEAF  SPOT  OF  STRAWBERRY 
Mycosphcerella  Fragarice  (Tul.)  Lindau 

DUDLEY,  W.  R.    On  the  Strawberry  Leaf-Spot.    Cornell  Agl.  Exp.  Sta.  Built. 

14:   171-184.    1889. 
SCRIBNER,  F.  L.    Strawberry  Leaf  Blight.    U.  S.  Dept.  Agl.  Rept.   (1887): 

334-341.    pi.  i, 

One  of  the  diseases  of  the  strawberry  most  frequently  met  with 
is  that  commonly  known  as  the  strawberry  leaf  spot.  The  disease 
makes  its  appearance  in  the  form  of  small,  discolored  spots,  ap- 
pearing upon  the  leaves  most  abundantly  about  the  time  of  flower- 
ing (Fig.  114).  At  first  these  spots  are  of  a  reddish  or  purplish 
tint,  but  as  they  increase  in  size  the  center  becomes  pale  and  may 
be  quite  white  when  the  death  of  the.  tissues  has  ensued.  This 
white  central  area  is  ordinarily  bordered  by  a  zone  of  red  and 
purple  in  different  shades.  These  spots  are  irregularly  distributed 
over  the  leaves,  and  when  numerous  they  may  coalesce.  All  of 
the  cultivated  varieties  of  strawberries  may  be  affected,  although 
there  is  considerable  difference  in  the  degree  of  susceptibility. 
Among  some  of  the  berries  most  susceptible  in  the  northeastern 
United  States  may  be  mentioned  the  Hunn  and  the  Beeder 
Wood.  Susceptibility  of  a  variety  varies,  however,  when  culti- 
vated under  different  conditions.  Marshall  and  Brandywine  have 
often  proved  very  resistant. 


262  FUNGOUS  DISEASES  OF  PLANTS 

The  fungus.  The  life  history  of  the  fungus  has  been  con- 
siderably studied,  and  it  is  probable  that  some  spore  stages  which 
have  been  described  are  not  at  any  rate  common  stages  in  the 
life  cycle.  In  general,  two  spore-producing  stages  may  be  found, 
the  conidial  and  the  ascigerous  stages.  The  conidial  stage  has 
been  described  as  Ramularia  Tulasnei.  This  appears  in  early 
summer,  as  a  rule,  or  so  soon  as  the  pale  centers  of  the  spots 
have  been  developed.  Small,  tuberculate  stromatic  masses  are 
produced  upon  the  mycelium  beneath  the  epidermis,  and  from 
these  arise  a  small  group  of  simple  hyphae,  which  rupture  the 


FIG.  114.   LEAF  SPOT  OF  STRAWBERRY 

epidermis  and  produce  conidia  which  may  become  one  or  several 
times  septate.    The  conidia,  according  to  Dudley,  measure  20- 

40  x  3-5 /*  (Fig-  US,  <*)• 

The  ascigerous  stage  is  not  so  commonly  found  and  is  in  no 
case  developed  until  late  summer.  A  membranous  perithecium, 
characteristic  of  this  family,  is  then  produced  within  the  leaf,  al- 
though at  maturity  a  considerable  part  of  the  perithecium  may  be 
exposed.  Relatively  few  asci  are  developed,  the  asci  containing 
invariably  eight  hyaline,  uniseptate  spores  with  acute  tips  (Fig.  115). 
It  would  appear  that  the  spores  are  not  ordinarily  mature  until 
late  winter,  or  at  least  not  ejected  until  that  time.  Moreover, 


ASCOMYCETES  263 

hibernation  is  supposed  to  be  effected  in  some  cases  by  means 
of  the  tuberculate  stromata,  which  retain  their  vitality  and  serve  as 
minute  sclerotia,  germinating  the  following  spring.  The  asci 
average  40/4  long,  and  the  spores 
measure  about  1 5  x  3-4  p. 

Control.  Healthy  plants  only 
should  be  set,  and  all  spotted 
leaves  should  be  pinched  off. 
A  thorough  spraying  with  Bor-  a  b 

deaux    mixture     may    be     given      FIG.  115.   MYCOSPHAERELLA  FRAGARI^, 
before  the  flowers  are  open,  when       CoNIDIAL  AND  ASCIGEROUS  STAGES 
necessary.    If  the  disease  is  serious  or  disastrous  late  in  the  season, 
its  reappearance  the  next  year  may  be  delayed  and  to  some  extent 
averted  by  mowing  off  the  leaves  and  burning  over  the  bed. 

XLIII.    LEAF-SPLITTING  BLIGHT  OF  SUGAR  CANE 
Mycosphczrella  stratiformans  Cobb 

COBB,  N.  A.    Fungous   Maladies  of   the   Sugar   Cane.     III.    Leaf-Splitting 
Blight.    Hawaiian  Sugar  Planters  Exp.  Sta.  Built.  5:  93-106.    1906. 

This  is  the  name  provisionally  applied  to  a  fungus  which 
causes  a  peculiar  leaf-splitting  of  sugar  cane  in  portions  of  the 
Hawaiian  Islands.  The  leaves  are  split,  and  in  severe  cases 
reduced  to  shreds.  The  ascogenous  stage  alone  has  been  re- 
ported. The  perithecia  are  produced  abundantly.  Diseased  stalks 
should  not  be  planted,  and  all  leaf  trash  from  an  affected  field 
should  be  destroyed.  What  appear  to  be  related  species  of  fungi 
have  been  described  as  injurious  to  cane  in  Java  and  in  La  Plata, 
Argentina. 

Mycosphaerella  Cerasella  Aderh.1  is  considered  to  be  the  ascog- 
enous form  of  Cercospora  Cerasella  Sacc.,  well  known  upon  the 
leaves  of  cherry,  sometimes  producing  a  shot  hole  effect  similar 
to  that  which  may  follow  any  leaf  spot  fungus  parasitic  upon 
species  of  Prunus. 

1  Aderhold,  R.  Mycosphaerella  cerasella  n.  spec.,  die  Perithecienform  von 
Cercospora  cerasella  Sacc.,  und  ihre  Entwicklung.  Ber.  d.  deut.  hot.  Ges.  18  : 
246-249.  1900. 


264 


FUNGOUS  DISEASES  OF  PLANTS 


XLIV.    APPLE  SCAB  AND  PEAR  SCAB 
Venturia  Pomi  (Fr.)  Wint.  and  Venturia  Pyrina  Aderh. 

ADERHOLD,  RUD.    Die   Fusicladien  unserer  Obstbaume.   Landwsch.   Jahrb. 

25:  875-914.  pis.  29-31.    1896;   Ibid.  29:   541-587.  pis.  9-12.    1900. 
BEACH,  S.  A.    Experiments  in  Preventing  Pear  Scab  in  1893.    N.  Y.  Agl. 

Exp.  Sta.  Built.  67:    183-204. 
CLINTON,  G.  P.    Apple  Scab.    111.  Agl.  Exp.  Sta.  Built.  67:   109-156.    1901. 

(Good  bibliography.) 
DUGGAR,  B.   M.    Some   Important  Pear  Diseases.    Cornell  Agl.  Exp.  Sta. 

Built.  145:  616-622.  figs.  168-170.    1898. 
LAWRENCE,  W.  H.    The  Apple  Scab  in  Western  Washington.    Washington 

Agl.  Exp.  Sta.. Built.  64:   1-24.  pis.  1,2.   1904. 
SMITH,  RALPH  E.    Pear  Scab.   Calif.  Agl.  Exp.  Sta.  Built.  163:   1-18.  Jigs. 

1-9.    1905. 

Two  important  fungous  diseases  popularly  known  as  apple  and 
pear  scab  have  received  at  the  hands  of  both  mycologists  and 

horticulturists  considerable 
attention  within  the  past 
thirty  years.  The  fungi 
causing  these  diseases  are 
very  closely  related,  al- 
though quite  generally  re- 
ferred to  two  distinct 
species.  The  conidial  form 
of  each  of  these  fungi  was 
first  found  parasitic  upon 
its  respective  host ;  hence 
these  fungi  have  long  been 
known  by  the  names  of 
these  conidial  forms,  Fusi- 
cladium  dendriticiim  and 
Fu  sic  I  a  din  m  Py  r  i  n  u  m . 
More  recently  an  ascomy- 

cetous  fungus,  Venturia  Pomi,  has  been  found  to  constitute  the 
perfect  stage  of  the  apple  scab  organism,  and  a  related  perithecial 
form,  Venturia  Pyrina,  has  been  connected  with  the  pear  scab 
fungus.  The  perithecial  stages  develop  saprophytically,  a  phe- 
nomenon characteristic  of  many  Ascomycetes. 

Distribution  and  climatic  relations.    In  the  United  States  both 
the  scab  of  the  apple  and  of  the  pear  are  widely  distributed. 


FIG.  116.  A  SEVERE  ATTACK  OF  PEAR  SCAB 
ON  FLEMISH  BEAUTY 


ASCOMYCETES  265 

Moreover,  the  data  at  hand  seem  to  indicate  that  they  occur 
in  all  countries  in  which  the  host  plants  are  commercially  grown. 
These  fungi  are  apparently  of  economic  importance  in  all  sec- 
tions of  the  United  States  where  the  weather  may  be  cool  and 
damp  during  portions  of  the  spring  and  summer.  In  the  northern 
portion  of  the  United  States  it  has  received  particular  attention 
at  the  agricultural  experiment  stations  of  Vermont,  New  York, 
Illinois,  also  California,  thus  indicating  a  very  general  distribu- 
tion. It  is,  however,  believed  to  be  equally  distributed  in  the 
Southeast,  but  in  that  section  it  has  received  less  attention,  per- 
haps on  account  of  the  fact  that  the  commercial  output  of  these 
fruits  has  not  been  a  factor  of  such  importance.  In  the  past  few 


FIG.  117.   THE  EFFECTS  OF  APPLE  SCAB  DURING  A  MOIST  SEASON 

years  these  diseases  have  become  a  menace  on  the  Pacific  Slope. 
All  investigators,  however,  are  agreed  that  cool,  moist  weather 
either  in  spring  or  summer  encourages  the  rapid  spread  of  the 
fungus,  while  hot  winds  quickly  suppress  it. 

Losses.  It  is  not  easy  to  estimate  the  average  losses  from  these 
fungi,  and  this  is  particularly  true  on  account  of  the  fact  that  the 
scab  fungi  are  more  or  less  superficial  in  their  effects.  In  severe 
cases  the  fruit  is  wholly  unmarketable,  but  in  too  many  cases 
scabby  fruit  is  regularly  put  upon  the  market  and  the  reduced 
prices  which  it  brings  are  not  estimated.  During  seasons  favor- 
able for  the  fungus,  probably  one  year  in  two,  the  losses  in  many 
sections  of  the  country  amount  to  a  reduction  in  price  or  total 
destruction  of  from  25  to  50  per  cent  of  the  entire  crop. 


266 


FUNGOUS  DISEASES  OF  PLANTS 


The  relation  of  host  and  fungus.  These  fungi  commonly 
affect  fruit  and  leaves,  but  they  may  also  be  found  upon  leaf 
stalks,  flowers,  and  twigs.  Upon  the  leaves  (Fig.  118)  in  each 
case  the  spots  are  more  abundant,  as  a  rule,  upon  the  lower 
surface.  Where  the  fungus  is  made  evident  by  an  olivaceous, 
velvety,  superficial  growth,  or  when  the  disease  is  very  abundant, 
both  surfaces  of  the  leaf  may  be  covered  and  considerable  curling 


FIG.  118.    APPLE  SCAB  ON  LEAVES:  DIFFERENT  TYPES  OF  INFECTION 

may  result.  Upon  the  fruit  there  are  at  first  small,  circular,  oli- 
vaceous spots,  especially  upon  the  pear,  but  as  a  rule  the  appear- 
ance changes  as  the  fungus  spreads,  the  epidermis  is  killed,  and 
the  familiar  scabby  spots  are  produced.  At  times  practically  the 
whole  fruit  may  show  indications  of  the  fungous  growth,  and  a 
general  puckering  of  the  tissues  may  result  in  an  abnormal  form 
of  the  fruit.  Some  varieties  of  pear  may  develop  cracks  or 
fissures  extending  halfway  to  the  core.  Fig.  116  shows  a  severe 
attack  of  scab  on  Flemish  Beauty. 


ASCOMYCETES 


267 


There  are  probably  no  varieties  of  the  pear  or  apple  which 
are  entirely  free  from  scab.  Nevertheless,  there  is  a  great  dif- 
ference in  susceptibility.  In  New  York,  Flemish  Beauty,  Sum- 
mer Doyenne,  Duchess,  Clairgeau,  Sheldon,  Seckel,  Anjou,  and 
Lawrence  have  been  reported  as  more  generally  affected  than 
Le  Conte,  Kieffer,  and  Bartlett.  In  California  the  later  varieties 
like  Winter  Nellis  and  Easter  Beurre  are  said  to  be  more  sus- 
ceptible than  the  Bartlett,  which,  however,  is  only  resistant  to 
an  intermediate  degree.  The  susceptibility  of  different  varieties 
of  apple  to  the  apple  scab  seems  to  vary  considerably  according 


FIG.  119.   CONIDIAL  STAGE:  FUSICLADIUM  OF  THE  PEAR  SCAB  FUNGUS 

to  the  region  in  which  grown,  yet  nearly  all  of  the  standard 
varieties  may  be  affected  during  seasons  favorable  to  the  fungus. 
The  fungus.  The  spores  of  the  Fusicladium  stage  germinate 
readily  in  water  and  develop  a  short  germ  tube,  or  sometimes 
two  germ  tubes.  The  germ  tube  sometimes  forms  a  dark  spore- 
like  structure,  if  the  conditions  are  not  favorable  for  further  rapid 
growth.  This  structure  is  scarcely  in  the  nature  of  an  appres- 
sorium,  and  may  be  considered  a  resting  stage,  which  will  grow 
out  into  mycelium  under  favorable  conditions.  It  is  believed  that 
the  mycelium  of  these  two  species  of  fungi  develops  for  a  short 
time  superficially,  then  penetrates  the  epidermis  in  some  way. 
At  any  rate,  the  mycelium  is  found  at  a  very  early  stage  beneath 


268  FUNGOUS  DISEASES  OF  PLANTS 

the  epidermis,  and  between  the  epidermis  and  cuticle.  In  these 
situations  it  spreads  slowly.  According  to  some  writers  the  prin- 
cipal development  at  first  is  immediately  beneath  the  cuticle. 
That  is  particularly  true,  according  to  reported  observations,  on 
the  leaves.  On  the  fruit,  however,  both  the  cuticle  and  the  epi- 
dermis are  soon  broken  and  disappear  as  the  spot  becomes  scabby 
in  appearance.  Upon  the  pear  I  have  quite  generally  found  the 
mycelium  to  be  subepidermal  at  the  edge  of  the  scabby  spots.  It 
may  form  a  layer  several  times  as  thick  as  the  diameter  of  the  hyphae, 
and  as  the  epidermis  wears  off,  this  mycelial  layer  is  exposed,  and 
beneath  this  the  cells  of  the  host  may  become  corky,  as  shown 
in  Fig.  119.  The  mycelium  is  olivaceous  or  sometimes  reddish- 
brown  in  color,  closely  septate,  sinuous  and  irregular  in  branching. 


FIG.  120.   GERMINATING  SPORES  OF  FUSICLADIUM 

The  olivaceous  growth  on  the  surfaces  of  the  fruits,  leaves,  and 
twigs  is,  however,  made  up  very  largely  of  the  short,  erect  conidio- 
phores.  These  conidiophores  arise  from  the  subcuticular  or  sub- 
epidermal  mycelium,  break  the  cuticle  if  the  latter  is  still  intact, 
and  a  spore  is  soon  developed  at  the  tip  of  each.  A  spore  may 
be  borne  when  the  conidiophore  has  attained  a  length  of  four  or 
five  times  its  diameter.  However,  when  this  spore  is  abscised, 
the  conidiophore  grows  further,  leaving  a  slight  knee  or  other 
evidence  indicating  the  point  where  the  previous  spore  was  borne. 
In  this  manner  many  successive  conidia  may  be  produced,  and 
the  conidiophore  therefore  becomes  flexuous  and  irregular.  It 
may  also  become  septate  in  time.  The  conidia  on  both  hosts 
measure  ordinarily  28-30  x  /-QA6-  They  are  more  or  less  ovate 
in  form,  the  basal  end  being  more  truncate.  They  are  ordinarily 
continuous  but  may  become  once  septate  with  age.  The  color  is 
fuliginous  or  olivaceous,  sometimes  having  a  slight  reddish  tint. 


ASCOMYCETES  269 

According  to  Clinton,  the  conidia  are  probably  unable  to  retain 
their  vitality  for  a  considerable  period  of  time,  and  therefore  may 
not  be  of  great  consequence  in  initiating  the  disease  the  following 
season.  Some  believe,  however,  that  the  scabby  spots  upon  old 
fruits  remain  living,  at  least  so  far  as  the  mycelium  is  concerned, 
and  that  new  conidia  may  be  produced  the  following  spring. 
They  would  believe  that  this  is  particularly  true  when  the  fungus 
has  attacked  young  twigs,  and  that  therefore  it  is  in  favorable  con- 
dition for  early  infection.  Nevertheless,  the  fungus  has  not  been 
found  constantly  or  abundantly  upon  young  twigs  and  it  is  quite 
probable  that  twig  infections  are  less  common  than  is  supposed. 
In  that  case,  the  constant  reappearance  of  the  disease  may  be 
more  generally  due  to  the  development  of  the  perfect  stage 
during  the  winter. 

So  far  as  the  development  of  the  perithecial  form  has  been 
followed  in  this  country,  it  is  believed  that  the  first  evidences  of 
the  perithecium  in  the  case  of  the  apple  scab  are  found  in  October 
and  later,  the  perithecia  reaching  maturity  by  April  perhaps.  At 
any  rate,  mature  ascospores  have  been  found  during  April  and 
May,  and  the  perithecia  disappear  by  the  following  month.  The 
perithecia  are  usually  found  on  the  under  surfaces  of  the  leaves, 
and  Clinton  believes  that  less  conspicuous  scabby  spots  develop 
the  perfect  stage  most  freely.  The  studies  which  have  been  made 
of  the  perithecia  in  artificial  cultures,  strengthened  by  the  obser- 
vations in  the  open,  seem  to  indicate  beyond  any  question  the 
relationships  of  these  two  forms.  The  perithecia  are  somewhat 
imbedded  in  the  tissues  of  the  leaf,  are  spherical  or  nearly 
spherical  in  form  (Fig.  121),  90  to  150^  in  diameter,  and  at 
maturity  slightly  beaked,  these  beaks  being  sometimes  protected 
by  half  a  dozen  or  more  bristles.  The  perithecial  wall  is  made  up 
of  cells  more  or  less  polygonal  in  outline.  The  asci  are  clavate  to 
oblong  or  slightly  curved,  55-75  X  6-12/JL.  They  are  numerous  in 
the  perithecia  and  so  far  as  noted  there  are  no  paraphyses.  The 
spores  are  eight,  becoming  two-celled,  one  of  which  is  larger  than 
the  other.  The  spores  are  olive-brown  in  color,  11-15  X  5-7  A6- 

The  histological  development  of  the  perithecium  has  not  been 
followed.  The  ascospores  germinate  readily  in  water,  and  some- 
times true  appressoria  are  produced,  as  stated  in  the  case  of  the 


270 


FUNGOUS  DISEASES  OF  PLANTS 


germination  of  the  conidia.  The  observation  has  been  made 
(Clinton)  that  the  scab  is  first  seen  more  abundantly  on  the  lower 
leaves,  and  from  this  the  inference  is  drawn  that  infection  is 
chiefly  as  a  result  of  the  production  of  the  perfect  or  Venturia 
stage  on  old  leaves  which  have  fallen  to  the  ground.  The  pro- 
duction of  the  perfect  stage  is  common  when  the  leaves  fall  upon 
sod  and  are  more  or  less  protected  by  their  own  number  or  by 
being  partially  covered  with  grass,  etc. 


FIG.  121.    VENTURIA  POMI,  FROM  WINTERED  LEAVES  OF  APPLE 

Control.  In  the  agricultural  experiment  stations  of  the  United 
States  spraying  experiments  have  been  quite  generally  conducted 
looking  toward  the  prevention  of  apple  and  pear  scab.  Some  dif- 
ferences in  treatment  have  been  recommended  for  regions  where 
climatic  relations  are  diverse,  but  in  general  the  method  of  treat- 
ment is  much  the  same.  At  least  one  spraying  should  be  made 
with  strong  Bordeaux  mixture  before  blossoming.  In  California 
it  has  been  recommended  to  spray  twice  before  the  fruit  buds 
have  opened ;  this  in  case  of  the  pear.  A  second  (or  third) 
spraying  may  be  given  immediately  after  the  petals  fall,  and  at 


ASCOMYCETES  271 

least  one  more  two  weeks  after  the  second.  The  conditions, 
however,  must  determine  the  length  of  time  intervening  and  the 
number  of  applications  made. 


XLV.    BITTER  ROT  OF  THE  APPLE  AND  OTHER  FRUITS 
Glomerella  rufomaculans  (Berk.)  Spauld.  &  Von  Sch. 

BLAIR,  J.  C.    Bitter  Rot  of  Apples.     111.  Agl.  Exp.  Sta.  Built.  117:  483-551. 

1907. 
BURRILL,  T.  J.    Bitter  Rot  of  Apples.    111.  Agl.  Exp.  Sta.  Built.  77  :  351-366. 

//.  C.    figS.  I-I2.      1902. 

BURRILL,  T.  J.    Bitter  Rot  of  Apples.   111.  Agl.  Exp.  Sta.  Built.  118  :  554-608. 

1907. 
CLINTON,  G.  P.  Bitter  Rot.  111.  Agl.  Exp.  Sta.  Built.  69  :  193-21 1.  figs.  1-39. 

1902. 
CLINTON,  G.  P.    Gnomoniopsis  fructigena.    111.  Agl.  Exp.  Sta.  Built.  69 :  206- 

211.    1902. 
EDGERTON,  C.  W.  The  Physiology  and  Development  of  Some  Anthracnoses. 

Bot.  Gaz.  45:  367-408.  pi.  n.  figs.  1-17.    1908. 
HALSTED,  B.  D.    Laboratory  Studies  of  Fruit  Decays.    N.  J.  Agl.  Exp.  Sta. 

Rept.   (1892):  326-330. 
SCHRENK,  H.  VON,  and  SPAULDING,  P.  The  Bitter  Rot  of  Apples.  U.  S.  Dept. 

Agl.,  Bureau  of  Plant  Industry,  Built.  44:    1-54.  pis.  1-9.    1903. 
(Consult  this  paper  for  more  complete  bibliography  on  the  bitter  rot.) 
SCOTT,  W.  M.    The  Control  of  Apple  Bitter  Rot.    U.  S.  Dept.  Agl.,  Bureau 

of  Plant  Industry,  Built.  93:    1-33.  pis.  1-8.    1906. 
STONEMAN,  BERTHA.    A  Comparative  Study  of  Some  Anthracnoses.    Bot. 

Gaz.  26:    69-120.    pis.  7-18.    1898.   (Glceosporium  fructigenum  Berk. 

pp.  71-74.   figs.  i-4,33-38,  83.} 

The  most  destructive  apple  disease  in  the  chief  apple-growing 
districts  of  the  United  States  is  unquestionably  the  bitter  rot. 
This  disease  varies  greatly  in  virulence  with  the  conditions, 
becoming  at  times  so  destructive  as  practically  to  annihilate  a 
crop  in  large  areas.  Fortunately,  it  does  not  appear  in  great 
quantity  until  midsummer,  and  then  if  the  conditions  are  un- 
favorable it  may  not  become  a  source  of  serious  loss. 

Distribution.  The  bitter  rot  fungus  is  widely  distributed  in 
the  United  States  east  of  and  including  Kansas,  Oklahoma,  and 
Texas.  It  seems  to  be  particularly  destructive  in  a  more  or  less 
central  area  extending  from  the  Atlantic  seaboard  in  Virginia 
westward  to  Oklahoma.  The  fungus,  however,  is  not  limited  to 
the  United  States,  and  is  probably  common  and  more  or  less 
injurious  in  all  apple-producing  countries.  It  is  certainly  known 


272  FUNGOUS  DISEASES  OF  PLANTS 

throughout  Europe,  Australia,  and  in  some  parts  of  Asia.  The 
commercial  relations  between  the  different  countries  have  doubt- 
less effected  its  very  general  distribution.  In  the  United  States 
it  has  been  known  for  nearly  half  a  century,  although  it  is  un- 
likely that  it  was  a  matter  of  commercial  importance  prior  to  the 
general  and  widespread  development  of  orcharding,  and  the  con- 
sequent more  or  less  contiguous  orchard  areas.  Certainly  for 
twenty  years  it  has  been  recognized  as  of  serious  economic 
importance  in  the  central  area  already  designated. 

Climatic  relations.  Evidences  of  the  effects  of  the  bitter  rot 
fungus  are  usually  found  in  July  and  August,  although  in  the 
case  of  early  summer  apples  in  the  far  South,  and  under  ex- 
ceptionably  favorable  conditions,  it  may  appear  much  earlier. 
In  common  with  most  fungi,  the  favorable  conditions  are  to 
be  found  in  warm,  sultry  weather  accompanied  by  rains,  condi- 
tions so  frequent  during  August  in  the  chief  bitter  rot  regions. 
During  seasons  thus  characterized  the  fungus  may  spread  with 
alarming  rapidity,  causing  enormous  devastation  within  a  period 
of  a  single  week,  —  this  length  of  time  being  therefore  sufficient 
under  such  circumstances  for  the  propagation  of  the  fungus 
probably  through  two  or  more  generations.  Von  Schrenk  states 
that  the  time  of  the  appearance  of  the  bitter  rot  is  probably 
influenced  by  the  following  factors:  (i)  age  of  the  fruits;  (2) 
temperature  and  humidity  of  the  air ;  (3)  presence  of  spore- 
distributing  centers.  The  canker  areas  of  the  twigs  are  said  to 
develop  somewhat  earlier  in  the  season  and  under  less  restricted 
conditions.  During  cold,  dry  summers  the  apple  is  notably  free 
from  bitter  rot,  even  though  the  fungus  may  have  been  un- 
usually common  the  previous  season.  Cold  weather  may  act 
either  as  a  preventive  or  as  a  check  to  the  development  of  the 
disease  after  a  favorable  season  for  infection. 

Losses.  It  would  be  impossible  to  state  the  average  loss  sus- 
tained by  the  apple-growing  industry  throughout  the  United 
States  as  a  result  of  the  ravages  of  this  fungus.  During  years 
when  the  disease  is  prevalent  the  loss  will  certainly  amount  to 
millions  of  dollars.  The  president  of  the  National  Apple  Grow- 
ers Association  estimated  the  losses  in  1900  at  $10,000,000. 
Burrill  reported  for  the  same  year  a  loss  in  four  counties  in 


ASCOMYCETES  273 

Illinois  amounting  to  $1,500,000.  Apple  growers  have  become 
so  thoroughly  informed  as  to  the  destruction  of  this  disease  that 
they  have  to  a  large  extent  adopted  the  remedies  recommended 
as  a  result  of  recent  investigations,  and  steps  are  now  very 
generally  taken  to  control  this  fungus.  This  general  interest 
which  has  been  awakened  will  doubtless  tend  to  diminish  losses 
in  future  years. 

Parts  of  the  plant  affected.  Upon  the  apple  the  bitter  rot 
fungus  is  active  chiefly  as  a  fruit  parasite,  although  branches 
may  also  be  affected.  The  first  appearance  of  the  fungus  within 


FIG.  122.    BITTER  ROT  OF  APPLE 

the  tissues  of  the  fruit  is  made  evident  by  a  small  brown  spot 
beneath  the  skin.  In  the  field,  commonly,  a  single  infection,  or 
at  most  a  few  infections,  are  to  be  found  upon  one  fruit.  Under 
exceptionally  favorable  conditions,  however,  numerous  infections 
may  occur.  In  any  case,  the  affected  spot  may  increase  rapidly 
in  size,  showing  constantly  a  more  or  less  circular  outline  with 
a  well-defined  margin.  So  soon  as  the  spot  has  attained  a  size 
of  one-fourth  inch,  more  or  less,  the  central  portion  of  the 
affected  area  is  sunken,  and  this  is  followed  by  the  further 
gradual  spread  of  the  fungus  throughout  the  fruit,  and  by  the 
appearance  of  pustules  as  subsequently  described  (Fig.  122).  The 
whole  portion  of  the  fruit  affected  by  the  fungus  is  decayed,  and 


274  FUNGOUS  DISEASES  OF  PLANTS 

the  fruit  near  a  decayed  area  is  invariably  bitter.  This  character, 
which  appears  to  be  quite  constant,  has  given  the  disease  its 
popular  name.  Affected  fruits  usually  fall  from  the  trees  after 
a  spot  has  attained  considerable  size.  Nevertheless,  in  excep- 
tional cases  the  diseased  fruits  may  hang  on,  and  when  the 
whole  fruit  has  decayed  as  a  direct  or  indirect  effect  of  the  fun- 
gus, they  become  dried,  and  to  these  fruits  the  term  "  mummy  " 
has  also  been  applied. 

The  bitter  rot  fungus  has  been  found  upon  various  varieties 
of  the  apple.  In  some  sections  it  is  reported  more  commonly 
upon  Ben  Davis  and  Grimes  Golden,  but  this  may  be  more 
'particularly  due  to  the  fact  that  these  varieties  were  more  gener- 
ally grown  in  the  regions  for  which  the  report  was  made.  The 
fungus  is,  in  fact,  notably  unrestricted  as  to  host.  The  apple 
is  unquestionably  the  fruit  most  injured,  yet  the  same  fungus 
may  be  parasitic  upon  the  grape,  peach,  pear,  tomato,  eggplant, 
and  pepper ;  at  least,  if  infection  experiments  alone  can  be 
trusted  to  indicate  what  may  take  place  in  nature,  the  hosts 
above  mentioned,  as  well  as  others,  are  all  susceptible. 

The  fungus.  The  life  history  of  this  fungus  includes  two 
stages,  one  an  imperfect  fungus,  or  properly  glceosporial  stage, 
which  is  commonly  produced  upon  the  fruit,  and  the  other 
an  ascigerous  stage,  which  may  occasionally  be  produced  upon 
a  fruit  or  twig,  and  readily  developed  in  artificial  cultures.1  It  is 
believed  that  the  early  infection  of  the  fruit  frequently  arises  from 
the  development  of  pustules  bearing  conidia  in  canker  areas,  the 
spores  falling  from  the  canker  areas  to  the  fruit  below.  It  has 
been  frequently  observed  that  affected  fruits  on  a  tree  may  map 
out  a  pyramidal  area,  at  the  cone  of  which  may  be  found  a 
cankered  limb.  Such  canker  areas  (Fig.  123)  apparently  develop 
the  conidia  early  in  the  season.  The  cankers  are  in  the  form 
of  sunken  areas  upon  twigs  or  limbs,  and  they  are  often  round 
or  oblong,  sometimes  several  inches  long,  the  bark  covering  such 
areas  being  cracked  and  broken.  The  bark  readily  dries  out  and 

1  As  a  result  of  his  studies  upon  the  fungus  causing  bitter  rot  Edgerton  states  : 
"  There  are  apparently  two  forms  on  the  apple.  These  are  separated  in  their  geo- 
graphical distribution  apparently  by  thermal  lines ;  the  southern  form  differs  from 
the  northern  considerably  in  cultural  characters  and  it  differs  also  slightly  in  the 
characteristics  of  the  perithecium  and  the  acervulus." 


ASCOMYCETES 


275 


adheres  closely  to  the  underlying  wood.  Moreover,  tne  develop- 
ment of  a  callus  layer  at  the  edge  of  the  dead  spot  gives  a  further 
emphasis  to  the  depression  produced  by  the  death  and  shrinking 
of  the  tissues  within  the  canker  spots.  The  canker  spots  are  sup- 
posed to  persist  for  at  least  two  years.  The  mycelium  of  the  fun- 
gus may  be  found  in  the  inner  bark  and  cambium.  As  previously 
suggested,  the  pustules  of  the  fungus  break  through  the  bark  in 
these  cankered  spots  early  in 
the  season. 

When  the  fruit  spots  have 
attained  a  size  of  one  fourth 
inch  or  more  in  diameter, 
there  may  appear  in  concen- 
tric lines  small  papillae,  which 
are  in  reality  the  pustules  of 
the  fungus.  The  pustules  are 
formed  by  the  development  of 
a  stromatic  mass  of  mycelium 
beneath  the  epidermis.  From 
this  stromatic  mycelium  there 
develops  a  cone-shaped  mass 
of  erect  hyphae  which  eventu- 
ally rupture  the  cell  walls. 
Meanwhile  there  are  produced 
from  the  numerous,  erect 
conidiophores  an  abundance 
of  conidia.  When  the  epider- 
mis is  ruptured,  these  conidia  emerge  as  a  waxy,  tendril-like  strand, 
which  may  be  at  first  pink  in  color,  becoming  gray  with  age.  The 
spores  are  then  imbedded  in  a  gelatinous  matrix  readily  soluble  in 
water.  Little  may  therefore  be  seen  of  the  strand-like  production 
of  the  spores  during  moist  weather,  or  even  during  a  period  of 
heavy  dews.  Fig.  124  shows  the  relation  of  the  conidiophores  to 
the  mycelial  stroma.  Examined  microscopically  the  conidia  are 
almost  hyaline,  though  having  a  slight  greenish  cast.  They  vary 
in  shape  from  ovate  to  oblong,  or  in  some  cases  even  slightly 
dumb-bell-shape.  In  general,  however,  they  are  ovoidal  and  vary 
greatly  in  size,  according  to  the  conditions  under  which  they  are 


FIG.  123.   CANKER  OF  THE  BITTER  ROT 
FUNGUS.  (Photograph by  Perley  Spaulding) 


276 


FUNGOUS  DISEASES  OF  PLANTS 


produced.  Some  observers  have  recorded  extreme  sizes,  6-40  x 
3^-7^.  More  frequently,  however  (Von  Schrenk),  they  are  12- 
16  x  4-6  fj>.  The  conidia  germinate  readily,  and  upon  germination 
almost  invariably  become  septate.  Under  unfavorable  conditions 
a  germ  tube  may  develop  at  its  tip  a  brown  resting  cell  termed  a 
secondary  conidium  or  appressorium.  It  is  believed  that  the  germ 
tube  may  obtain  entrance  to  the  fruit  through  the  uninjured  skin 
of  the  apple,  and  certainly  artificial  infection  may  result  without 
noticeable  surface  injury.  Nevertheless,  infection  can  be  hastened 
by  injuring  the  surface,  and  it  is  possible  that  some  slight  injury  or 
abrasion  may  be  essential  to  penetration,  although  the  belief  is  cur- 
rent that  entrance  may  be  effected  through  the  stomates  of  the  fruit. 


FIG.  124.    GLOMERELLA  RUFOMACULANS:  CONIDIAL  AND  ASCIGEROUS  STAGES 

This  imperfect  form  was  for  a  long  time  the  only  known  fruiting 
stage  of  the  fungus.  It  was  referred  to  the  genus  Gloeosporium 
and  was  generally  known  as  Gloeosporium  fructigenum  Berk. 

The  perithecial  stage  of  this  fungus,  found  by  Clinton  in  1902, 
may  be  readily  developed  in  artificial  culture,  though  Clinton  has 
also  reported  having  found  it  frequently  upon  the  fruit.  In  cul- 
tures it  may  be  developed  within  two  weeks  on  various  nutrient 
media,  while  in  nature  it  develops  apparently  only  the  following 
spring  upon  fruit  which  has  been  upon  the  ground  throughout  the 
winter.  In  artificial  culture  the  perfect  stage  develops  promptly 
and  vigorously  upon  apple  agar  corn  meal.  The  mycelium  first 
forms  small  black  nodules  which  become  stromatic  cushions  about 
one  fourth  inch  in  diameter.  Within  this  stroma  one  or  many  peri- 
thecia  might  be  developed.  The  various  stages  in  the  development 


ASCOMYCETES  277 

of  the  perithecium  have  not  been  very  carefully  followed,  although 
it  would  appear  that  the  formation  of  asci  in  the  perithecium  is  pre- 
ceded by  a  central  mass  of  hyaline  cells,  which  are  displaced  as 
the  asci  arise.  At  maturity  the  asci  are  oblong-clavate,  5  5-70  x  9 p. 
Each  ascus  contains  eight  spores,  frequently  arranged  in  pairs, 
though  sometimes  in  oblique  series.  The  ascospores  are  curved, 
but  in  general  resemble  the  conidia.  They  are,  however,  more  uni- 
form in  size,  being  usually  12-22  x  3|— 5/*.  The  asci  are  evanes- 
cent, and  the  ascospores  germinate  without  a  period  of  rest. 

It  is  not  believed  that  the  ascus-bearing  stage  is  at  all  essential 
to  the  annual  appearance  of  this  disease.  It  has  been  frequently 
shown  that  the  conidia  in  mummied  apples  retain  their  vitality 
until  the  following  season,  and  it  is  probable  that  infection  could 
result  from  conidia  produced  on  apples  which  have  remained  on 
the  ground  throughout  the  winter.  However,  when  all  mummied 
fruits  in  the  trees  as  well  as  under  the  trees  have  been  carefully 
destroyed,  the  disease  has  been  found  abundantly  the  following 
season.  It  is  therefore  probable  that  a  great  many  infections  re- 
sult through  canker  spots  formed  during  the  summer.  These  live 
over  winter  and  produce  conidia  again  during  the  early  summer. 

Cultural  relations.  This  fungus  may  be  readily  cultivated  in 
the  laboratory  on  almost  any  of  the  ordinary  nutrient  media. 
Apple  agar  is  especially  favorable,  but,  as  already  indicated,  apple 
corn  meal  agar  is  perhaps  as  good  as  any  other  medium  for  the 
production  of  the  ascosporic  stage.  The  conidia  germinate  within 
a  few  hours  and  the  mycelium  grows  with  great  rapidity.  The 
mycelium  is  septate,  and  neighboring  cells  of  different  mycelia 
readily  fuse.  In  the  tissues  of  the  apple  the  hyphae  are  brown 
with  age.  In  culture,  however,  the  hyphae  are  at  first  only 
slightly  colored.  The  conidia  are  produced  in  quantity  in  culture, 
appearing  upon  an  agar  plate  within  twelve  hours.  Under  such 
conditions  the  conidia  are  generally  borne  upon  numerous  lateral 
branches.  Upon  sterilized  fruit  in  the  laboratory  the  production 
of  conidia  within  the  pustules  has  required,  under  the  most  favor- 
able conditions,  only  forty-eight  hours.  It  is  evident  therefore 
that  in  the  field  many  generations  of  this  fungus  may  be  pro- 
duced within  a  very  short  time,  and  that  its  rapid  spread  is  well 
explained  by  the  brief  period  required  for  spore  production. 


278  FUNGOUS  DISEASES  OF  PLANTS 

Control.  It  is  of  unquestionable  value  to  keep  the  orchard  as 
clean  as  possible  of  apples  affected  with  the  bitter  rot  fungus, 
and  it  is  likewise  important  to  prune  out  all  cankered  limbs. 
Nevertheless,  these  precautions  alone  are  wholly  insufficient,  and 
it  has  recently  been  demonstrated  that  the  disease  may  be  con- 
trolled —  at  least  under  the  conditions  prevailing  in  the  eastern 
United  States  —  by  a  proper  application  of  Bordeaux  mixture. 
Under  conditions  favorable  for  the  spread  of  the  disease,  from 
93.3  to  98.9  per  cent  of  sound  fruit  has  been  harvested  upon 
sprayed  trees,  while  the  controls  gave  practically  no  fruit  of  value. 
It  is  recommended  to  make  about  four  applications  of  Bordeaux 
mixture,  although  one  or  two  additional  applications  may  be 
necessary.  In  this  as  in  all  other  such  work,  the  tree  should  be 
thoroughly  sprayed  from  a  nozzle  giving  a  mist-like  application. 
When  spraying  for  bitter  rot  alone  the  first  application  may  be 
made  about  forty  days  after  the  petals  have  fallen,  subsequent 
applications  being  given  about  two  weeks  apart.  During  very  wet 
weather,  however,  greater  frequency  may  be  required,  while  in 
cool  weather  the  length  of  time  may  be  increased.  Beneficial 
results  from  spraying  experiments  have  also  been  obtained  in  the 
central  West,  and  it  is  believed  that  there  the  disease  may  be 
controlled  by  the  methods  suggested. 

XLVI.    ANTHRACNOSE  OF  SYCAMORE 
Gnomonia  Veneta  (Sacc.  &  Speg.)  Kleb. 

EDGERTON,  C.  W.  The  Physiology  and  Development  of  Some  Anthracnoses. 
Bot.  Gaz.  45:  367-408.  pi.  IT.  Jigs.  /-//.  1908. 

KLEBAHN,  H.  Unters.  iiber  einige  Fungi  imperfecti  u.  d.  zugehorigen  As- 
corny  cetenformen.  Jahrb.  f.  wiss.  Bot.  41 :  515-558.  1905. 

SCRIBNER,  F.  L.  A  Disease  of  the  Sycamore.  U.  S.  Dept.  Agl.  Rept.  (1888) : 
387-389.  pi.  75. 

SOUTHWORTH,  E.  A.  Glceosporium  nervisequum  (Fckl.)  Sacc.  Journal  My- 
cology 5 :  51-52.  1889. 

Habitat  relations.  This  fungus  is  parasitic  upon  the  leaves 
and  young  shoots  of  the  sycamore  or  plane  tree,  Platanns 
occidentalis,  and  it  is  widely  distributed  in  Europe  and  America. 
In  one  or  more  stages  the  fungus  also  appears  to  produce  spots 
upon  the  leaves  of  several  species  of  oak,  being  reported  upon 
Quercus  alba,  Quercus  vehitina,  and  Quercus  coccinea.  Upon 


ASCOMYCETES   '  279 

the  sycamore  it  is  in  one  stage  primarily  a  disease  of  the  leaf 
veins,  although  commonly  the  death  of  considerable  portions  of 
the  lamina  adjacent  soon  follows.  In  another  stage  the  fungus' 
is  notably  fatal  to  shoots,  young  trees,  and  seedlings.  According 
to  Edgerton  this  fungus  may  produce  in  the  early  spring  an 
effect  very  similar  to  frost  .injury.  Indeed,  these  injuries  have 
been  referred  by  several  to  spring  frosts.  On  the  whole  this  is 
one  of  the  most  disastrous  anthracnose  diseases  known,  and  far 
greater  attention  would  be  directed  to  it  if  greater  concern  were 
felt  for  the  sycamore,  which  is,  nevertheless,  a  most  important 
shade  tree. 

The  fungus.  The  interesting  life  history  of  this  fungus  has 
been  carefully  worked  out.  There  are  three  types  of  imperfect 
fungi  as  well  as  the  ascigerous  form  in  the  life  cycle  of  this  organ- 
ism. A  typical  Glceosporium  stage  (see  Glceosporium)  appears 
upon  the  leaves,  and  the  pustules  or  acervuli  are  well  developed 
upon  the  veins  of  both  the  upper  and  lower  surfaces.  Upon 
small,  colorless  conidiophores  ovate  conidia  are  produced  measur- 
ing 10-15  x  4-6  /4.  The  acervuli  are  from  100  to  300  ji  in  diam- 
eter, and  the  spores  are  produced  in  such  quantity  that  in  moist 
weather  they  are  forcibly  ejected  in  creamy  masses  or  strings. 
This  stage  has  long  been  known  to  mycologists  as  Glceosporium 
nervisequiim.  Upon  the  twigs  the  size  and  type  of  acervulus  has 
caused  the  fungus  to  be  referred  to  the  form  genus  Myxosporium. 
The  further  growth  of  the  stroma  later  in  the  season  may  develop 
the  pycnidial  or  Sporonema  stage,  in  which  similar  small  conidio- 
phores are  developed  from  all  sides  of  a  more  or  less  chambered 
pycnidium.  The  ascigerous  stage  is  abundantly  developed  on 
affected  leaves  which  have  wintered  over  in  the  open.  This  stage 
may  appear  either  during  late  winter  or  early  spring.  The  peri- 
thecia  vary  greatly  in  size,  but  are  ordinarily  from  150  to  250/4 
in  diameter,  with  beak  50-100/4  long.  The  asci  are,  according  to 
Edgerton,  48-60  x  12-15/4.  They  are  broadly  clavate  and  bent 
at  right  angles  near  the  base.  The  apex  is  thickened,  and  there 
is  a  terminal  pore  surrounded  by  a  more  refractive  ring.  The 
ascospores  are  invariably  eight;  they  are  hyaline,  elliptical  or 
arcuate,  once  septate,  and  composed  of  a  large  upper  cell  and 
a  small  lower.  The  germ  tube  emerges  invariably  from  the  larger 


280  FUNGOUS  DISEASES   OF  PLANTS 

cell.  The  various  spore  forms  of  this  fungus  have  yielded  in  cul- 
ture a  perfectly.  similar  mycelium,  and  infection  experiments  seem 
'to  leave  no  doubt  as  to  the  genetic  relationship. 

Control.  Preventive  measures  might  at  least  apply  to  nursery 
stock  and  to  young  trees  recently  set.  It  may  be  supposed  that 
thorough  applications  of  the  5~5~5°  Bordeaux  very  early  in  the 
season  would  greatly  assist  in  the  control  of  this  disease. 

XLVII.    A  DISEASE  OF  YOUNG  OAKS 
Rosellinia  Quercina  Hartig 

HARTIG,  ROBT.    Die  Eichenwurzeltodter.    Unters.  a.  d.  forst.-bot.   Inst.  Miin- 
chen(i88o):    1-32.  pis.  1,2. 

This  fungus  occurs  as  a  parasite  of  seedlings  and  young  oak 
trees  in  Germany.1  It  affects  primarily  the  roots  and  the  basal 
portion  of  the  stem.  It  has  been  prevalent  in  northwestern 
Germany  and  particularly  disastrous  when  it  occurs  in  the  seed 
beds.  The  greater  amount  of  injury  results  to  seedlings  from  one 
to  three  years  old.  The  effects  of  the  fungus  are  manifest  by  an 
unhealthy,  pale  color  of  the  foliage,  followed  by  withering  and 
wilting  of  the  leaves.  Young  shoots,  and  subsequently  the  older 
leaves,  also  wither  and  die.  About  the  roots  and  sometimes  the 
lower  portion  of  the  stem  will  be  found  a  felt-like  mycelium  of 
interwoven  brown  threads,  or  strand-like  aggregations. 

The  perithecia  are  commonly  produced  in  quantity,  particularly 
after  the  death  of  the  plant.  They  are  spherical  or  ovate  in  form, 
and  brittle  in  texture,  with  a  papillate  ostiolum.  The  asci  are  long- 
cylindrical,  each  containing  eight  elliptical  or  somewhat  fusiform, 
brown  or  brown-black  spores,  which  are  ordinarily  vacuolate,  and 
measure  28  x 


1  One  or  two  other  species  of  Rosellinia  have  been  described  as  important 
from  the  disease  point  of  view.  Prillieux  (Comp.  Rend.  135  :  275.  1902)  found 
a  form  on  the  roots  of  fruit  trees  accompanying  Dematophora,  which  he  considers 
to  be  the  perfect  stage  of  the  latter.  He  believed  that  the  perithecia  were  developed 
on  the  stroma  on  which  arose  the  conidiophores.  The  perithecia  measure  1.5  mm. 
in  diameter,  are  gray-brown  in  color,  with  a  definite  and  darker  papilla.  The  body 
is  composed  of  three  wall  layers,  —  the  outer  indurated  and  brown,  the  central 
white,  and  the  inner  yellowish  in  color.  From  the  latter  arise  the  stalked  asci, 
365-380  X  8.5-9/4,  and  small  slender  paraphyses.  The  spores  long  remain  color- 
less, but  are  finally  black  with  small  vacuoles. 


ASCOMYCETES  281 

XLVIII.    BARK  DISEASE  OF  CHESTNUT 
Diaporthe  parasitica  Murrill 

METCALF,  HAVEN.  The  Immunity  of  the  Japanese  Chestnut  to  the  Bark 
Disease.  Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  121 :  55-56.  1908. 

MURRILL,  W.  A.  A  Serious  Chestnut  Disease.  Jour.  N.  Y.  Bot.  Garden  7 : 
143-153.  figs.  13-19.  1906.  (Also  7:  203-211.  Jigs.  25 -jo.  1906.) 

MURRILL,  W.  A.  A  New  Chestnut  Disease.  Torreya  6 :  186-189.  fig.  2. 
1906. 

Occurrence.  This  bark  disease  of  the  chestnut  has  recently 
been  reported  from  New  York,  New  England,  and  other  north- 
eastern states,  and  it  would  appear  that  it  is  spreading  rapidly. 
It  is  in  fact  becoming  a  serious  menace  to  forest  tree  culture  in 
that  section  of  the  country.  The  common  species  of  chestnut 
(Castanea  dentatd),  seems  to  be  in  all  localities  peculiarly  sus- 
ceptible, and  so  far  as  the  observations  go,  all  species  of  the 
genus  Castanea  are  subject  to  it  with  one  exception,  this  excep- 
tion being  certain  Japanese  varieties  of  Castanea  crenata  Sieb. 
and  Zucc.  Metcalf  has  found  the  latter  to  be  quite  generally 
immune,  and  while  the  nuts  are  inferior  in  flavor  to  the  best 
European  varieties,  it  is  nevertheless  an  important  commercial 
product.  It  is  hoped  that  hybridization  between  the  Japanese  and 
American  or  European  forms  will  be  successful  in  establishing 
immune  varieties  with  other  desirable  characteristics  of  the  better 
sorts.  It  is  not  believed,  however,  that  the  Japanese  chestnut 
can  to  any  extent  replace  the  native  tree  for  forest  purposes, 
although  the  former  is  desirable  from  an  ornamental  standpoint. 
It  is  suggested  that  since  the  Japanese  chestnut  was  first  intro- 
duced on  Long  Island,  it  is  possible  that  Japan  may  be  the  home 
of  this  fungous  pest,  and  that  as  a  result  no  resistance  could  have 
been  developed  in  the  native  species. 

The  fungus.  The  fungus  has  been  found  upon  twigs,  small- 
sized  branches,  and  trunks.  It  completely  encircles  the  affected 
limbs,  and  the  girdling  thus  brought  about  ultimately  causes  the 
death  of  portions  beyond,  and  lessened  vitality  of  the  whole  tree. 

The  mycelium  of  the  fungus  is  confined  very  largely  to  the 
bark  and  to  the  underlying  cambium.  The  affected  cortex  be- 
comes somewhat  light  brown  in  color  and  slightly  sunken  after 
desiccation. 


282  FUNGOUS  DISEASES  OF  PLANTS 

Infection  does  not  seem  to  be  possible  through  uninjured 
outer  bark,  but  when  the  latter  is  punctured  or  broken,  the 
fungus  promptly  penetrates  the  living  tissues.  It  is  inferred, 
therefore,  that  infection  occurs  through  wounds  and  possibly 
through  lenticels. 

During  the  summer  there  is  developed  through  the  lenticels 
from  a  stromatic  mycelium  the  imperfect  stage  of  the  fungus. 
This  latter  produces  small,  rod-like  but  curved  spores,  character- 
istic of  the  genus  Cytospora  of  the  imperfect  fungi.  These  spores 
are  discharged  in  long,  twisted,  brownish,  thread-like  masses.  This 
stage  serves  for  the  very  rapid  propagation  of  the  disease. 

During  autumn  there  may  be  produced  from  the  stroma  in  the 
inner  bark  the  perithecial  stage.  The  latter  appear  in  clusters  of 
from  ten  to'  twenty.  They  are  flask-shaped  with  long,  slender 
necks  protruding  above  the  surface.  The  asci  are,  according  to 
Murrill,  45-50  X  9/u.  They  are  constantly  eight-spored,  hyaline, 
oblong,  two-celled,  and  measure  9-10  x  4-5^. 

Control.  No  practical  method  of  controlling  this  fungus  has 
been  suggested.  Severe  pruning  is  certainly  advisable  if  the  dis- 
ease is  detected  when  twigs  or  branches  alone  are  infested,  and  it 
is  possible  that  systematic  effort  may  hold  the  disease  in  check, 
even  where  the  conditions  are  favorable  for  its  spread.  Spraying 
is  perhaps  impracticable. 

XLIX.    BLISTER  CANKER  OF  APPLE 
Nummularia  discreta  Tul. 

HASSELBRING,  H.   Canker  of  Apple  Trees.   111.  Agl.  Exp.  Sta.  Built.  70 :  225- 
239.  pis.  1-4.    1902. 

The  blister  canker  of  the  apple  is  well  distributed  throughout 
the  apple-growing  region  of  the  Mississippi  Valley,  and  doubtless 
in  other  sections  of  the  United  States.  It  also  occurs  in  Europe, 
but  has  not  been  reported  as  a  disease  worthy  of  special  consider- 
ation. This  canker,  like  others  already  described,  is,  however,  a 
source  of  constant  danger  on  account  of  the  fact  that  it  is  per- 
ennial in  the  host  and  in  time  is  sure  to  cause  the  death  of  large 
limbs  or  of  the  entire  tree.  The  blister  canker  has  been  termed 
the  Illinois  canker,  since  it  was  first  observed  as  particularly 


•ASCOMYCETES 


283 


destructive  in  that  state.  Under  ordinary  circumstances  the  fungus 
is  doubtless  a  mere  saprophyte,  and  it  is  not  restricted  to  the  apple 
or  to  other  members  of  the  apple  family.  It  has  in  fact  been  found 
upon  such  trees  as  the  following :  American  elm  (Ulmus  americana\ 
Magnolia  sp.,  Judas  tree  (Cercis  canadensis),  and  Sorbus  sp. 

Symptoms.  The  disease  is  usually  found  upon  the  larger  limbs 
or  upon  the  trunk,  and  the  appearance  of  the  canker  areas  is  so 
characteristic  that  it  cannot  be 
mistaken,  at  least  in  late  stages 
of  the  disease,  for  any  of  the 
cankers  thus  far  discussed. 
At  first  the  infested  areas  are 
brown,  slightly  sunken,  and  con- 
sist of  small  spots  of  healthy 
tissue  intermingled  within  the 
general  diseased  area.  These  die 
later,  but  there  is  an  irregular 
and  mottled  effect  which  per- 
sists and  is  readily  observed. 
The  infected  .area  may  cover 
many  square  inches  of  surface, 
and  it  is  sharply  delimited  from 
the  healthy  tissue,  due  to  the 
drying  and  cracking.  Occa- 
sionally there  is  a  slight  de- 
velopment of  slime  during  the 
early  part  of  the  season,  but 
this  has  not  been  associated  with  the  action  of  the  parasite. 

Hasselbring  describes  the  external  appearance  during  the  late 
season  as  follows  : 

The  bark  of  the  older  parts  becomes  much  roughened  and  blackened  as  if 
it  had  been  charred.  Numerous  rifts  and  cracks  appear  over  the  surface  of  the 
dead  bark,  which  is  very  dry  and  brittle,  and  falls  off  in  irregular  patches,  ex- 
posing the  dead  wood.  The  circular  stromata  are  firmly  attached  to  the  wood 
by  means  of  a  ring  of  hard  fungous  tissue,  so  that  they  remain  seated  on  the 
wood  even  after  the  bark  has  fallen  away.  The  entire  blackened  area  is  dotted 
over  with  the  circular  stromata,  which  form  the  most  pronounced  distinguishing 
feature  of  this  canker.  The  disease  is  always  easily  recognized  by  these  stromata 
(Fig.  1 25),  which  distinguish  it  clearly  from  the  New  York  apple  tree  canker. 


FIG.  125.   BLISTER  CANKER  OF  APPLE 


284 


FUNGOUS  DISEASES  OF  PLANTS 


The  fungus.  The  mycelium  penetrates  the  bark  and  later  the 
wood  beneath  to  a  considerable  extent.  The  course  of  the  fungus 
through  the  bark  and  wood  is  very  largely  through  the  paren- 
chymatous  and  medullary  cells.  From  these,  however,  it  infests 
neighboring  tissues,  especially  the  xylem  vessels.  The  stromata 
and  fruit  bodies  are  developed  from  the  latter  part  of  the  summer 
into  the  autumn  and  winter.  From  the  upper  surface  of  the 
stroma  a  mat  of  conidial  hyphae  arises.  These  break  through  the 

epidermis  and  underlying  fun- 
gous tissue.  The  conidia  are 
simple,  hyaline  spores  which 
apparently  do  not  readily  ger- 
minate. Later  in  the  season 
the  underlying  stromatic  tis- 
sue which  is  now  cup-shaped 
shows  the  development  of 
flask-shaped  perithecia  sunken 
in  that  portion  of  the  stroma 
which  is  made  up  chiefly  of 
fungous  tissue.  Bordering  the 
stroma  a  black  line  of  more 
abundant  fungous  tissue  is 
also  evident.  The  body  of  the 
perithecium  is  elliptical  or 
ovate  at  maturity,  and  it  is  com- 
pletely filled  with  long-cylin- 
drical asci  about  160  x  13/4. 
The  asci  are  thick-walled  with 
terminal  pore,  and  contain  at  maturity  eight  more  or  less  spher- 
ical, brown  spores.  The  latter  often  measure  13  x  IO/A,  and  a  clear 
space  along  one  side  indicates  the  line  of  rupture  during  germina- 
tion. Twin  germ  tubes  are  invariably  developed. 

Control.  Observations  on  the  progress  of  this  disease  would 
seem  to  indicate  that  this  fungus  gains  entrance  through  wounds, 
and  prevention  consists  in  avoiding  as  far  as  possible  the  im- 
proper injuries  due  to  careless  methods  of  pruning,  cultivation, 
and  harvesting.  Moreover,  the  cankered  areas  on  limbs  should 
be  pruned  out  and  destroyed  when  found. 


FlG.  126.    NUMMULARIA  DISCRETA  :  THE 
BLISTER  CANKER  FUNGUS 

a,  stroma ;    b,  perithecium  ;  c,  ascus 


CHAPTER    XII 

FUNGI  IMPERFECTI 

The  imperfect  fungi,  or  fungi  imperfecti,  constitute  an  heter- 
ogeneous subdivision  of  the  true  fungi.  As  a  class  it  is  not  com- 
parable to  the  natural  classes  thus  far  discussed,  yet  it  may  be 
given  an  equivalent  name  and  regarded  as  a  coordinate  division 
for  the  sake  of  convenience  in  general  treatment  and  classifica- 
tion. The  fungi  thus  brought  together  consist  of  species  hav- 
ing hyphomycetous,  melanconiaceous,  or  sphaeropsidaceous  types 
of  spore  production.  Since  these  types  may  represent  special 
"  stages  "  in  the  life  cycles  of  other  fungi,  these  secondary  fruit 
forms  in  general  will  not  permit  of  certain  classification  under  the 
groups  thus  far  discussed,  much  less  under  the  Basidiomycetes 
subsequently  treated.  The  great  majority,  however,  and  perhaps 
all  of  those  here  discussed  would  unquestionably  find  their  natural 
relationships  with  various  genera  of  the  Ascomycetes,  and  for  that 
reason  they  are  conveniently  treated  as  following  that  group. 
Some  of  the  Hyphomycetes  in  general,  however,  might  represent 
imperfect  forms  of  the  Phycomycetes  or  even  of  the  Basidio- 
mycetes. In  any  case  it  would  generally  be  impossible  to  de- 
termine the  genus  or  even  the  family  in  which  a  particular 
imperfect  fungus  or  form  genus  might  be  placed.  It  is  therefore 
essential  to  have  such  form  genera,  under  which  species  may  be 
described  and  classified  until  their  complete  life  cycles  are  known, 
when  they  may  be  transferred  to  the  proper  natural  genus  (genus 
of  so-called  perfect  fungi).  In  many  other  minor  ways  the  form 
genus  is  a  matter  of  convenience  and  certainly  contributes  some 
stimulus  for  a  better  description  of  the  different  spore  forms  in 
the  polymorphic  species. 

Among  the  imperfect  fungi,  as  here  interpreted,  three  chief 
subdivisions  are  generally  recognized,  as  follows  : 

Hyphomycetes  —  conidia  borne  upon  exposed  conidiophores 
which  may  be  single,  fascicled,  or  united  together  in  a  columnar 
or  tubercular  fashion. 

285 


286  FUNGOUS  DISEASES  OF  PLANTS 

Melanconialas  —  conidia  borne  on  relatively  short  conidiophores 
arising  from  or  within  a  more  or  less  differentiated  stroma,  pro- 
duced usually  beneath  the  epidermis. 

Sphceropsidales  —  conidia  borne  on  short  conidiophores  arising 
within  a  perithecium,  or  pycnidium,  or  sometimes  within  cavities 
of  a  dense  stroma. 

The  primary  subdivisions  of  these  groups  are  termed  families, 
and  in  the  case  of  the  Sphaeropsidales  this  classification  is  based 
on  characters  more  or  less  comparable  to  those  separating  certain 
orders  or  families  of  the  Ascomycetes.  The  secondary  and  further 
subdivisions  down  to  the  genera  are  properly  an  artificial  classifi- 
cation based  chiefly  upon  the  color  of  the  spores  and  the  extent 
of  septation.  Details  of  this  classification  may  be  found  in  the 
taxonomic  works ;  but  a  brief  comparison  of  important  genera 
embracing  parasitic  species  is  here  included. 

I.  HYPHOMYCETES 

I .  (Mucedinece  ;  mycelium  and  spores  generally  light  colored.) 

Oospora.  In  this  genus  the  vegetative  mycelium  is  delicate  and 
inconspicuous.  The  conidia  are  relatively  numerous,  ovoidal  to 
spherical  in  form,  hyaline,  and  unicellular  (amerosporic). 

Monilia.  In  this  case  the  vegetative  hyphae  are  more  evident 
and  the  fertile  hyphae  are  branched,  often  in  dense  clusters,  with 
hyaline  or  slightly  colored  conidia  produced  in  chains.  To  this 
form  genus  the  conidial  stage  of  the  brown  rot  of  stone  fruits 
may  be  referred  (cf.  Sclerotinia  fructigena). 

Oidium.  As  generally  interpreted  this  genus  includes  among  its 
representatives  the  conidial  stage  of  Erysiphaceae  (cf.  page  215). 
The  powdery  mildew  of  the  vine  was  long  known  only  as  Oidium 
Tiickeri.  The  '  conidia  are  produced  in  chains  on  short,  erect 
hyphae  generally  arising  from  a  superficial  mycelium. 

Sporotrichum  possesses  an  extensive  mycelium  and  conidio- 
phores which  are,  as  a  rule,  well  differentiated.  The  latter  are 
branched  and  bear  numerous,  hyaline,  one-celled,  more  or  less 
spherical  conidia.  These  originate  from  tips  of  branches  or  on 
minute  sterigmata.  Some  species  of  this  genus  parasitic  or  sapro- 
phytic  upon  insects  are  connected  with  a  compound  form,  Isaria, 
and  an  ascigerous  stage,  Cordyceps, 


FUNGI  IMPERFECTI  287 

Botrytis.  This  genus,  although  somewhat  indefinitely  character- 
ized, differs  from  the  preceding  chiefly  in  having  spores  grouped 
at  the  tips  of  branches  and  ordinarily  borne  on  papillae  or  tooth- 
like  projections. 

Cephalothecium  is  characterized  by  relatively  long,  unbranched, 
upright  conidiophores,  at  the  tip  of  each  of  which  may  be  produced 
a  cluster  of  two-celled,  hyaline  (hyalodidymic),  usually  pear-shaped 
conidia. 

Ramularia.  The  mycelium  is  wholly  within  the  tissues  of  the 
host,  the  conidiophores  are  hyaline,  straight  or  flexuous,  single  or 
fascicled.  The  conidia  are  single  or  loosely  adherent  in  chains. 
They  are  narrowly  elliptical  to  cylindrical,  and  divided  into  three 
or  more  cells  (hyalophragmic). 

Cercosporella.  This  genus  is  related  to  the  preceding  on 
account  of  its  hyaline  conidiophores  and  conidia,  but  on  the 
other  hand  it  is  very  close  to  Cercospora,  subsequently  described, 
on  account  of  the  filiform  spores  (scolecosporic)  and  sometimes 
geniculate  conidiophores. 

Piricularia  differs  from  the  preceding  genus  in  having  conidia 
which  are  strongly  obclavate  to  pyriform  and  generally  pluriseptate. 

2 .  (Dematieae ;  mycelium  dark,  at  least  with  age  ;  spores 
generally  dark.) 

Fusicladium.  The  mycelium  produces  short  conddiophores 
which  may  be  single  or  in  small  clusters.  These  produce  at 
the  tips  elliptical  conidia  which  at  maturity  are  two-celled  and 
colored  (phaeodidymic)  (cf.  Venturia,  page  264). 

Polythrincium  differs  from  the  last-mentioned  genus  chiefly  in 
the  nodulose  or  twisted  conidiophores. 

Scolecotrichum.  These  forms  possess,  instead  of  nodulose 
conidiophores,  those  which  are  geniculate,  a  knee  being  formed 
as  the  conidiophore  is  prolonged  by  growth  on  one  side  of  each 
spore  successively  produced.  The  spores  are  more  or  less  ellip- 
tical and  two-celled. 

Cladosporium.  In  this  genus  there  is  less  regularity  in  the 
form  of  the  conidiophores  and  the  sizes  of  spores,  as  the  conidio- 
phores are  considerably  branched,  and  these  branches  may  be- 
come spores.  The  conidiophores  are  olivaceous,  also  the  ovate, 
eventually  two-celled  conidia. 


288  FUNGOUS  DISEASES  OF  PLANTS 

Helminthosporium  possesses  straight,  dark  colored  conidio- 
phores  bearing  club-shaped  or  spindle-form,  many-celled,  flavous 
to  dark  colored  conidia  (phaeophragmic). 

Macrosporium.  In  this  genus  the  straight  conidiophores  bear 
ovoidal  or  elliptical  spores  which  are  transversely  septate,  and 
many  of  the  cells  thus  formed  become  longitudinally,  and  then 
even  again  transversely,  divided  (dictyosporic). 

Alternaria  differs  from  the  previous  genus  particularly  in  hav- 
ing the  conidia  borne  in  chains,  and  these  conidia  are  often 
clavate  in  form. 

Cercospora  possesses  straight,  flexuous,  or  strongly  geniculate 
conidiophores,  which  may  be  single  or  grouped.  The  conidia 
are  needle-shaped  or  filiform  (scolecosporic),  hyaline  to  considera- 
bly colored,  and  from  three  to  many  times  septate.  This  is  one 
of  the  largest  genera  of  the  Hyphomycetes,  containing  about  five 
hundred  described  species,  more  than  three  fourths  of  which  are 
attributed  to  North  America.  All  species  are  parasitic. 

3.  ( Tubercularice ;  conidiophores  in  the  form  of  a  tuberculate 
mass,  or  sporodochium). 

Volutella.  In  this  genus  the  sporodochium,  or  fruiting  tubercle, 
is  a  more  or  less  closed,  disciform  body,  not,  however,  produced 
on  a  basal  stroma.  It  is  provided,  around  the  border,  with  hair- 
like  setae.  The  conidiophores  are  mostly  unbranched  and  give 
rise  terminally  to  hyaline,  unicellular  conidia. 

Fusarium.  In  this  genus  the  sporodochia  are  small  cushion- 
like  masses  of  interwoven  hyphae  which  may  appear  waxy  or  fila- 
mentous in  texture.  The  conidiophores  proper  are  unbranched, 
and  they  bear  successively  at  the  tips  curved  or  sickle-shaped, 
hyaline,  many-celled  (at  maturity)  conidia. 

II.  MELANCONIALES 

Glceosporium.  The  spore-producing  pustule,  or  acervulus,  may 
be  extensive,  and  is  made  up  of  a  mass  of  relatively  short  conidio- 
phores arising  from,  and  commonly  partially  inclosed  within,  a 
stromatic  cushion  of  fungous  tissue.  At  maturity  the  stroma 
opens,  and  thus  it  ruptures  the  epidermis.  It  may  even  expand 
so  widely  as  to  seem  to  constitute  merely  a  basal  stroma.  The 
spores  are  ovoidal,  fusiform,  or  slightly  curved,  and  hyaline 


FUNGI  IMPERFECT!  289 

(hyalosporic).  There  are  supposedly  about  three  hundred  species,  all 
of  which  are  parasitic.  Some  species  are  connected  with  Glomerella 
or  related  genera  (cf.  Glomerella  rufomaculans •,  page  271). 

Colletotrichum,  including  about  forty  species,  has  characters 
similar  to  the  preceding  except  that  the  acervuli  are  bordered  by 
from  few  to  many  dark,  rigid  setae,  usually  several  times  the 
length  of  the  conidiophores. 

Marssonia  is  a  genus  similar  in  development  to  Glceosporium 
except  that  it  possesses,  as  a  rule,  less  extensive  acervuli,  two- 
celled  (hyalodidymic)  spores,  and  it  occurs  on  leaves  only. 

Septogloeum  is  another  genus  of  the  Glceosporium  type  except 
that  the  long-elliptical  or  cylindrical  conidia  are  pluriseptate. 

Coryneum  is  characterized  by  simple  conidiophores  and  dark, 
triseptate  or  pluriseptate  conidia  (phaeophragmic)  without  append- 
ages of  any  kind.  The  conidia  are  not  set  free  in  horn-like  or 
tendril-like  masses. 

Pestalozzia  is  readily  distinguished  by  the  peculiar  conidia, 
which  are  more  or  less  elliptical,  triseptate  or  pluriseptate,  the 
apical  and  basal  cells  being  hyaline  or  very  light  colored,  and  the 
central  cells  dark.  The  apical  cell  is  provided  with  one  or  more 
filiform  appendages.  The  conidiophores  are  also  filiform. 

Cylindrosporium  is  comparable  to  Septogloeum  except  that  the 
spores  are  filiform  or  needle-shaped,  usually  curved  and  continuous. 

III.  SPH/EROPSIDALES 

Phoma.  In  members  of  this  genus  the  pycnidia  are  single,  or 
sometimes  closely  aggregated.  They  are  immersed  in  the  tissues 
of  the  host  until  maturity,  when  the  epidermis  is  ruptured.  The 
conidia  are  small,  hyaline,  usually  ovate  or  elliptical,  and  continu- 
ous. The  genus  is  arbitrarily  limited  to  those  species  having 
spores  less  than  15/4,  larger  forms  being  relegated  to  Macro- 
phoma.  Species  of  Phoma  inhabit  fruits,  twigs,  or,  in  some 
cases,  all  parts  of  the  hosts,  but  they  are  considered  to  produce 
no  definite  spots.  About  eleven  hundred  species  of  this  genus 
are  recognized,  but  relatively  few  of  these  have  been  determined 
by  broad  comparison  or  careful  cultural  studies. 

Phyllosticta  applies  to  species  similar,  morphologically,  to  those 
in  the  preceding  genus.  Phyllosticta,  however,  produces  definite 


290  FUNGOUS  DISEASES  OF  PLANTS 

spots  and  inhabits  leaves  only.  This  is  also  a  very  large  genus, 
consisting  of  about  eight  hundred  species. 

Forms  of  both  Phyllosticta  and  Phoma,  occurring  on  the  grape, 
have  been  found  to  be  stages  of  a  Guignardia.  Some  species  of 
Phoma  would  seem  to  be  imperfect  stages  of  Diaporthe,  and 
others  have  been  associated  with  still  other  ascigerous  forms. 

Sphaeropsis  includes  species  with  relatively  large,  continuous, 
colored  conidia  (phaeosporic).  The  conidia  are  generally  elliptical. 
The  pycnidia  are  at  first  immersed  and  finally  break  through  the 
epidermis.  They  are  black  with  papillate  ostiolum.  There  are 
nearly  two  hundred  species  of  this  genus,  of  which  a  few  are 
important  parasites. 

Coniothyrium,  which  includes  nearly  as  many  species  as 
Sphaeropsis,  differs  from  the  latter  chiefly  in  the  smaller  size  of 
the  spores,  which,  moreover,  are  often  less  colored. 

Septoria.  In  this  genus  the  pycnidium  resembles  closely  that 
of  Phyllosticta  or  Sphaeropsis,  but  the  spores  are  long  and  fili- 
form, often  slightly  curved,  usually  pluriseptate.  With  respect  to 
spore  characters,  therefore,  the  genus  corresponds  more  or  less 
to  Cercosporella  and  Cylindrosporium  of  the  imperfect  fungi 
here  described. 

Leptothyrium  is  characterized  by  a  more  or  less  superficial, 
shield-shaped,  black  pycnidium  without  definite  ostiolum.  The 
spores,  are  one-celled  and  hyaline. 

Entomosporium  possesses  relatively  large,  black  pycnidia  with- 
out ostiola.  The  spores  are  four-celled  in  the  form  of  a  cross,  the 
horizontal  cells  smaller.  Each  cell  is  provided  with  a  delicate  awn- 
like  appendage. 

IV.    POTATO  SCAB 

Oospora  scabies.  Thaxter 

STURGIS,  W.  C.  On  the  Susceptibility  of  Various  Root  Crops  to  Potato  Scab, 
etc.  Conn.  (N.  H.)  Agl.  Exp.  Sta.  Kept.  20 :  263-266. 

THAXTER,  ROLAND.  The  Potato  "  Scab.'r  Conn.  Agl.  Exp.  Sta.  (1890): 
81-95. 

THAXTER,  ROLAND.  The  Potato  Scab.  Conn.  Agl.  Exp.  Sta.  (1891):  153-160. 

The  scab  of  potatoes  is  a  disease  which  is  well  known  to  grow- 
ers, dealers,  and  consumers  alike,  for  the  conspicuous  scab  pits  or 
spots  on  the  surface  of  tubers  cannot  fail  to  strike  the  attention. 


FUNGI  IMPERFECTI  291 

The  disease  is  most  common  throughout  the  United  States,  and 
doubtless  throughout  the  potato-producing  regions  of  Europe  as 
well.  It  is  not  positively  demonstrated,  however,  that  all  of  the 
surface  injuries  known  as  scab  are  properly  referable  to  the  fungus 
here  discussed  as  the  causal  organism,  yet  it  is  highly  probable  that 
potato  scab  as  a  common  disease  is  generally  due  to  Oospora  scabies. 
Sturgis  and  others  have  found  turnips  (Bras  sic  a  campestris], 
beets,  and  mangels  (Beta  vulgaris]  susceptible  to  this  disease.  Car- 
rots (Daucus  Carotd]  and  parsnips  (Pastinaca  sativa)  are  not  re- 
garded as  susceptible.  It  is  possible,  moreover,  that  this  fungus 


FIG.  127.   POTATO  SCAB 

may  occur  upon  the  less  conspicuous  roots  of  some  other  plants, 
but  it  is  typically  a  disease  of  fleshy  roots. 

Before  the  scab  organism  had  been  isolated  and  careful  inocu- 
lation experiments  made,  a  great  variety  of  causes  were  assigned 
by  observers  and  investigators,  various  bacteria  and  fungi,  also 
insects  and  myriapods  being  held  responsible  for  these  injuries. 

The  result  of  Thaxter's  studies  in  1 890  furnished  proof  that  the 
common  form  of  scab  in  New  England  is  caused  by  a  minute  par- 
asitic fungus  tentatively  designated  as  above.  The  disease1  "  first 
shows  itself  as  a  minute  reddish  or  brownish  spot  on  the  surface 

l  Thaxter,  /.  c.,  1890. 


292 


FUNGOUS  DISEASES  OF  PLANTS 


of  the  tuber,  often  making  its  appearance  when  the  tuber  is  very 
young,  and  sometimes  not  until  it  has  reached  a  considerable  size. 
This  discoloration  very  commonly,  though  not  invariably,  has  its 
origin  in  one  of  the  roughened  points,  or  lenticels,  which  are  scat- 
tered over  the  surface  of  the  potato,  and  after  it  has  once  appeared 
may  extend  quite  rapidly  to  the  adjacent  tissue,  becoming  deeper 

in  color  and  being  associated 
with  an  abnormal  corky  de- 
velopment of  the  parts  in- 
volved, which  often  cover  a 
considerable  area.  This  area 
may  constitute  a  more  or  less 
irregular  scab-like  crust  over 
the  surface,  or  more  fre- 
quently may  become  deeply 
cracked  and  furrowed,  the 
depth  and  extent  of  the  injury 
depending  in  a  great  meas- 
ure upon  the  stage  at  which 
the  tuber  first  became  dis- 
eased ;  those  which  are  at- 
tacked while  very  young 
showing,  as  might  be  ex- 
pected, by  far  the  most  deep 
seated  injury"  (Fig.  127). 

If  scabby  potatoes  are 
carefully  harvested  and  im- 
mediately examined,  there 
will  be  found  associated  with 
the  disease  an  evanescent 
grayish  film.  This  film  is  made  up  of  extremely  delicate,  minute, 
refractive,  branched  filaments,  which  break  up  into  bactericidal 
cells.  Some  branches  are  curved,  and  spore-like  structures  are 
also  produced  within  certain  cells. 

Experiments  demonstrate  that  the  fungus  may  persist  in  the  soil 
several  years.  A  few  scabby  potatoes  are  sufficient  to  spread  the 
organism  to  a  bin  of  clean  tubers.  To  secure  potatoes  free  of  scab, 
clean  tubers  should  be  planted  in  soil  free  from  the  fungus. 


FIG.  128.   A  SUGAR  BEET  AFFECTED  WITH 
SCAB 


FUNGI  IMPERFECTI 

Control.  Abundant  experimental  work  has  shown  that  of  the 
two  possible  lines  of  control,  soil  treatment  or  seed  treatment,  the 
latter  is  most  effective ;  and  this,  together  with  a  judicious  rota- 
tion of  crops,  is  sufficient  permanently  to  control  this  disease. 
The  method  of  treating  the  seed  tubers  consists  in  immersing 
them  for  two  or  more  hours  in  a  solution  of  i  ounce  of  formalin 
to  every  2  gallons  of  water,  or  in  a  solution  of  bichloride  of  mer- 
cury, consisting  of  I  ounce  to  8  gallons  of  water. 

V.    BUD  ROT  OF  CARNATIONS 
Sporotrichum  Poce  Pk. 

HEALD,  F.  D.    The  Bud  Rot  of  Carnations.    Neb.  Agl.  Exp.  Sta.  Built.  103 : 

pis.  1-8.    1908. 
STEWART,  F.  C.,  and  HODGKISS,  H.  E.    The  Bud  Rot  of  Carnations  and  the 

Silver  Top  of  June  Grass.    N.  Y.  (Geneva)  Agl.  Exp.  Sta.,  Tech.  Built. 

7:  83-119.  pis.  1-6.    1908. 

Habitat  relations.  The  bud  rot  of  carnations  has  recently 
received  careful  attention  as  of  importance  in  some  of  the  green- 
houses of  New  York,  Illinois,  and  Nebraska.  In  cases  where  the 
infection  is  late  in  developing,  or  where  the  conditions  are  un- 
favorable for  the  fungus,  the  infected  flowers  may  be  only  slightly 
abnormal  or  disfigured.  Even  in  these  cases,  however,  the  petals 
become  eventually  discolored,  and  the  death  of  the  calyx  also  en- 
sues. In  severe  attacks,  or  under  favorable  conditions  for  the 
fungus,  there  is  developed  within  the  bud  a  soft  rot,  resulting 
in  discoloration  of  all  the  parts.  Occasionally  the  evidences  of 
fungous  growth  are  sensible  to  the  unaided  eye. 

Commonly  there  is  associated  with  the  fungus  a  species  of 
mite.  According  to  the  experimental  evidence,  this  mite  has  no 
causal  connection  with  the  disease,  but  it  is  doubtless  of  im- 
portance in  the  distribution  of  the  fungus.  In  an  early  stage 
of  the  attack,  the  mites  are  extremely  minute,  and  might  be  over- 
looked ;  but  later  the  distention  of  the  mite  body  makes  it  an 
object  of  such  size  that  it  may  not  be  overlooked  even  upon 
casual  observation.  Experiments  have  clearly  indicated  that  the 
fungus  is  able  to  produce  the  disease  when  inoculated  in  the 
young  buds  by  needle  prick  or  scalpel  wound. 


294 


FUNGOUS  DISEASES  OF  PLANTS 


The  fungus  has  been  isolated  and  can  be  readily  grown  in 
artificial  media.  Upon  starchy  media,  or  media  containing  con- 
siderable sugar,  it  produces  a  very  vigorous  growth,  often  cottony 
in  appearance.  Glucose  agar,  corn  meal,  etc.,  are  colored  pink, 
or  some  shade  of  deep  red  after  growth  of  a  week  or  more ;  but 
the  color  is  less  intense  when  the  fungus  is  grown  on  starchy 
products,  apparently,  than  on  a  glucose  agar. 

The  fungus.  It  produces  two  forms  of  conidia,  which  have 
been  designated  microconidia  and  macroconidia  (Fig.  129).  The 
microconidia  are  more  or  less  subspherical,  or  slightly  pointed  at 
the  base,  even  pear-shaped,  and  they  are  produced  by  a  constric- 
tion from  lateral  or 
terminal  branches,  the 
latter  being  sometimes 
clustered.  Each  branch 
may  produce  a  large 
number  of  conidia  by 
successive  abscision, 
and  the  conidia  fre- 
quently become  massed 
together  in  balls.  They 
vary  from  5.5  to  S/JL 
in  diameter,  and  are 
capable  of  immediate 
germination,  producing  a  much  branched  mycelium.  The  macro- 
conidia are  far  less  frequent  in  culture  and  in  nature  than  the 
microconidia.  The  method  of  production  of  the  former  type  is 
practically  the  same  as  in  the  case  of  the  microconidia.  There  is, 
however,  greater  vacuolation  of  the  protoplasmic  contents  during 
the  formation  of  the  macroconidia,  which,  moreover,  may  become 
ovoidal,  and  finally  further  elongate,  becoming  once  or  more  septate. 
They  measure  4.5-5.8  x  10-17.5/1.  Owing  to  the  fact  that  the 
conidia  are  in  general  microconidia,  properly  the  type  of  the  genus 
Sporotrichum,  this  fungus  is  retained  in  that  genus. 

Control.  This  disease  is  often  one  of  serious  importance  in 
well-arranged  and  sanitary  carnation  houses  ;  but  it  is  apparently 
most  to  be  feared  where  conditions  for  forcing  the  host  are  desired, 
or  where  unsanitary  conditions  prevail.  Control  or  prevention 


FIG.  129.   SPOROTRICHVM  PosF. :  CONIDIOPHORES 
AND  CONIDIA 


FUNGI  IMPERFECTI  295 

therefore  concerns  itself  primarily  with  a  maintenance  of  condi- 
tions as  dry  and  cool  as  is  compatible  with  satisfactory  growth, 
and  also  with  matters  of  general  sanitation,  such  as  proper  ven- 
tilation, destruction  of  diseased  parts,  and  all  defective  specimens, 
leaves,  and  other  refuse.  Affected  buds  should  also  be  picked 
off  and  burned.  Susceptible  varieties  should  not  be  grown  where 
the  disease  prevails. 

VI.    A  PINK  ROT  FOLLOWING  APPLE  SCAB 
Cephalothedum  roseum  Cda. 

CRAIG,  JOHN,  and  VAN  HOOK,  J.  M;    Pink  Rot.   An  Attendant  of  Apple  Scab. 

Cornell  Univ.  Agl.  Exp.  Sta.  Built.  207:    199-210.  figs,  36-40.    1907. 
EUSTACE,  H.  J.    A  Destructive  Apple  Rot  Following  Scab.    N.  Y.  Agl.  Exp. 

Sta.  Built.  227  :   367-389.  pis.  1-8.    1902. 


FIG.  130.   PINK  MOLD  FOLLOWING  APPLE  SCAB.   (Photograph  by  John  Craig) 

During  several  seasons,  particularly  the  autumn  of  1902,  apple 
scab  was  very  prevalent  in  western  New  York,  favored  by  a  moist, 
muggy  season.  The  scab  was  followed  in  the  autumn  by  the  devel- 
opment of  a  mold  upon  the  scab  spots  (Fig.  130),  which  was  at 
first  white,  becoming  pink  with  a  production  of  abundant  spores. 
The  fungus  was  identified  as  above,  and  proved  to  be  common  in 
many  orchards  of  the  state.  It  is  a  widely  distributed  saprophyte, 
which  can  be  expected  perhaps  to  cause  widespread  injury  only 
when  conditions  are  unusally  favorable  for  its  development.  The 
greatest  damage  is  done  after  harvesting,  and  the  Rhode  Island 
Greening  has  proved  to  be  the  variety  most  susceptible  to  its  attack. 


296 


FUNGOUS   DISEASES  OF  PLANTS 


Inoculation  experiments  have  also  indicated  that  this  fungus  may 
produce  a  rot  through  wound  infections  on  apple,  pear,  quince,  and 
grape.  It  is  believed  that  the  fungus  will  become  injurious  only 
under  the  conditions  mentioned,  and,  therefore,  it  is  necessary  to 
take  indirect  precautions  only.  Prevention  of  the  scab,  in  particular, 
will  mean  prevention  of  this  rot,  which  is  secondary  to  it. 

VII.    RAMULARIA 

While  the  genus  Ramularia  is  entirely  parasitic,  few  plant  dis- 
eases of  serious  consequence  are  produced.    Reference  has  already 


FIG.  131.    CEPHALOTHECIUM 
ROSEUM 


FIG.  132.   AREOLATE  MILDEW  OF 
COTTON 


been  made  to  Ramularia  Tulasnei  (see  Mycosphcerella  Fragarice, 
page  261). 

Ramularia  areola  Atk.  This  fungus,  producing  what  may  be 
known  as  the  frosty  blight  or  "  areolate  mildew  "  of  cotton,  is  very 
characteristic.  Small  areas  of  the  leaf  between  the  finer  veinlets 
are  .occupied  by  the  fruiting  hyphae.  The  latter  are  fascicled,  and 
numerous  spores  are  borne.  As  a  result  of  the  abundance  of  the 
fruiting  hyphae  and  the  avoidance  of  the  veins  an  areolate  appear- 
ance is  presented  (Fig.  132). 


FUNGI  IMPERFECTI  297 

Ramularia  rufomaculans  Pk.  This  Ramularia  produces  on  the 
leaves  of  buckwheat  (Fagopyrum  esculentum}  blotch-like  areas  cov- 
ered with  abundant  conidiophores.  In  appearance  it  is  therefore 
very  much  like  the  form  on  cotton. 

VIII.    CERCOSPORELLA 

Cercosporella  Persicae  Sacc.  The  frosty  mildew  of  the  peach  in 
the  United  States  is  far  more  common  from  Maryland  southward. 
It  forms  on  the  under  surfaces  of  the  leaves  conidiophores  and 
conidia  in  such  quantity  as  to  give  the  appearance  of  a  surface 
mildew.  It  is  most  prevalent  and  often  a  serious  disease  in  moist 
regions,  but  may  be  readily  controlled  by  early  spraying. 

IX.    RICE  BLAST 
Piricularia  grisea  (Cke.)  Sacc. 

FULTON,  H.  R.    Rice  Blast.    La.  Agl.  Exp.  Sta.  Built.  105:   1-12.  figs.  1-12. 

1908. 

FARNETI,  R.    Rivista  Patalog.    Veg.  2 :   1-11,17-42. 
METCALF,  HAVEN.    Preliminary  Report  on  the  Blast  of  Rice.     S.  C.  Agl. 

Exp.  Sta.  Built  121  :    1-43.    1906. 

Habitat  relations.  The  blast  of  rice  (Oryza  sativa)  is  reported 
from  the  most  important  rice-growing  regions,  and  would  appear 
to  be  a  common  disease  wherever  rice  is  cultivated.  It  causes  no 
small  annual  loss,  and  the  outbreaks  are  frequently  severe.  Up  to 
the  present  time  there  is  very  little  unanimity  in  the  opinions  ex- 
pressed with  respect  to  the  factors  conditioning  epidemics.  After 
an  analysis  of  diverse  conditions  reported  as  operative,  Fulton 
believes  that  the  factors  are  far  more  complex  than  generally 
stated.  In  South  Carolina  it  seemed  that  unfavorable  soil  con- 
ditions are  important,  and  in  Italy  lack  of  root  aeration  is  sug- 
gested as  the  cause  of  "brusone,"  a  disease  with  which  the 
Piricularia  is  at  least  associated. 

Under  favorable  conditions  there  is  a  marked  difference  in  the 
susceptibility  of  diverse  rice  varieties.  At  the  present  time  it  would 
seem  that  there  are  no  varieties  wholly  free  from  the  disease. 

Symptoms.  The  fungus  attacks  leaves  and  stems.  Upon  young 
plants  the  older  leaves  are  first  affected  and  later  the  younger  por- 
tions of  the  plant.  The  young  leaves  become  rapidly  pale  in  the 


298  FUNGOUS  DISEASES  OF  PLANTS 

affected  areas  and  then  water-soaked,  dark  and  dead.  Conspicuous 
lesions  occur  at  the  sheath  nodes  and  upon  the  stems.  When  the 
disease  appears  at  or  above  the  topmost  stem  node,  it  is  generally 
most  serious.  The  maturing  heads  droop  or  fall  to  the  ground. 
Leaves  affected  at  the  tip  of  the  sheath  also  hang  downward.  Old 
leaves  may  develop  spots  with  ash-colored  centers  and  bright 
brown  borders. 

The  fungus.  Conidiophores  and  conidia  of  the  fungus  may  be 
found  abundantly  upon  the  affected  parts  in  moist  weather.  The 
former  emerge  from  the  stomata,  generally  in  clusters  of  two  or 
three.  They  are  ordinarily  simple,  fuliginous  in  color,  septate, 
and  they  bear  in  succession  several  conidia,  each  from  a  tip 
which  is  for  the  time  terminal.  The  spores  are  ovate,  two-septate, 
and  measure  24-29  x  10-12 /A.  Careful  inoculation  experiments 
have  shown  that  the  fungus  is  able  to  induce  the  disease  in  unin- 
jured, growing  plants  of  various  ages.  The  fungus  on  rice  was 
described  as  Piricularia  Oryzce  Briosi  &  Cavara,  but  the  evidence 
available  indicates  that  the  fungus  concerned  is  identical  with 
Piricularia  grisea,  as  above  given.  The  latter  is  the  name  applied 
to  the  fungus  occurring  in  many  regions  upon  the  crab  grass 
(Panicum  sanguinale  LI). 

Control.  It  is  unquestionably  important  in  rice  culture  to  pro- 
vide the  most  favorable  conditions  for  a  vigorous  growth  of  the 
rice  plant,  and  at  present  other  direct  preventive  measures  seem 
impracticable.  It  would  seem  that  varietal  resistance  will  in  time 
offer  the  safest  means  of  control. 

X.    POLYTHRINCIUM 

Polythrincium  Trifolii  Kzc.  Sooty  spot  of  clover.  This  fungus 
is  very  generally  distributed  upon  certain  species  of  clover,  notably 
red  clover  (Trifolium  pratense\  in  many  parts  of  the  world.  The 
wavy  or  spiral  character  of  the  conidiophores  and  the  sooty  or 
fuliginous  color  of  conidia  and  conidiophores  are  characteristic. 
This  species  is  the  only  one  which  has  been  described  in  the  genus. 
On  account  of  the  characteristics  and  habits  of  the  mycelium  and 
of  the  stroma  sometimes  produced,  it  has  been  assumed  that  the 
perfect  stage  would  be  a  species  of  Phyllachora,  and  the  plant 
actually  bears  also  the  name  Phyllachora  Trifolii  (Pers.)  Fckl. 


FUNGI  IMPERFECTI  299 

XI.    PEACH  AND  APRICOT  SCAB 
Cladosporium  carpophilum  Thiim. 

ARTHUR,  J.  C.    Spotting  of  Peaches.     Ind.  Agl.  Exp.  Sta.  Built.  19:   1-8. 

figs.  1-3.    1889. 
CHESTER,  F.  D.    Peach  Scab.    Del.  Agl.  Exp.  Sta.  Rept.  8:  60-63.    1896. 


FIG.  133.   PEACH  SCAB  ON  WHITE-FLESHED  FRUIT 

This  fungus  is  responsible  for  the  well-known  peach  scab,  a 
disease  common  throughout  the  country  on  peaches,  and  also  on 
apricots.  It  forms,  as  a  rule,  numerous 
small,  circular,  sooty  spots,  sometimes 
confined  to  one  portion  of  the  fruit  and 
at  other  times  scattered  over  the  whole 
surface.  It  is  so  common  upon  the 
poorer  grade  of  market  fruit  that  dur- 
ing an  ordinary  season  practically  none 
of  the  second  or  third  quality  fruit,  es- 
pecially that  with  white  pulp,  is  free 
from  it.  The  spots  may  become  scabby 
in  form,  and  coalesced  into  large  irreg- 
ular areas,  and  as  a  result  of  the  injury 
severe  cracking  of  the  fruit  may  occur 
(Fig.  133).  Twigs  and  leaves  may  also 
become  affected.  On  the  latter  distinct 
spots  are  produced,  often  accompanied 
by  the  falling  out  of  the  affected  areas, 
as  with  many  other  fungi,  thus  leaving 
a  shot-hole  effect.  On  the  twigs  the 


FIG.  134.    CLADOSPORIUM 
CARPOPHILUM 


FUNGOUS  DISEASES  OF  PLANTS 


fungus  may  be  perennial  in  brown  or  purplish-brown  spots,  and 
from  such  areas  the  conidial  stage  of  the  fungus  is  produced  the 
following  spring.  The  fungus,  shown  in  Fig.  134,  is  known  only  by 
the  conidial  stage,  and  the  latter  is  developed  throughout  the  season. 
In  artificial  culture  this  Cladosporium  grows  readily,  producing  a 
dense  olive-black  mycelium,  with  somewhat  abnormal  conidiophores 
and  conidia,  but  no  other  stage  has  been  reported  in  such  cultures. 

XII.    CLADOSPORIUM:  OTHER  SPECIES 
Cladosporium  Cucumerinum  Ell.  and  Arth.    This  fungus,  like 
many  other  species  of  the  genus,  is  occasionally  parasitic.    It  occurs 

upon  melons,  producing 
sunken  spots  on  the  fruit, 
and  sometimes  on  the 
stems.  This  trouble  is  ap- 
parent, as  a  rule,  only  dur- 
ing very  moist  weather, 
and  under  such  circum- 
stances the  conidial  stage 
of  the  fungus  is  developed 
abundantly  over  the  af- 
fected areas,  which  ap- 
pear olivaceous  in  color 
(Fig.  135). 

Cladosporium  fulvum 
Cke.  Leaf  mold  of  tomato. 
This  fungus  is  common 
during  moist  weather,  pro- 
ducing on  tomatoes  a  leaf 
blight  which  shows  itself 
in  its  effects  upon  the  up- 
per surface  by  a  moderate 
yellow  discoloration,  which  may  eventually  appear  as  true  spots. 
On  the  under  surface  the  olivaceous  growth  of  the  fungus  may 
be  seen.  As  the  disease  progresses  the  entire  leaf  may  become 
yellowed,  and  often  whole  plants  may  be  defoliated.  The  fungus 
is  an  active  parasite,  although  belonging  to  a  genus  most  of  the 
members  of  which  are  saprophytic  in  habit. 


FIG.  135.    CLADOSPORIUM  CUCUMERINUM  ON 
MELON 


FUNGI  IMPERFECTI  301 

XIII.    EARLY  BLIGHT  OF  THE  POTATO 
Macrosporium  Solani  E.  &  M. 

CHESTER,  F.  D.    A  Leaf  Blight  of  the  Potato.    Del.  Agl.  Exp.  Sta.  Rept.  4 : 

58-60.    1891. 
GALLOWAY,  B.  T.   The  Macrosporium  Potato  Disease.    Agl.  Sci.  7  :  370-382. 

1893. 

JONES,  L.  R.    Potato  Blights.    Vermont  Agl.  Exp.  Sta.  Rept.  9:  66-88.   1895. 
JONES,  L.  R.    Certain  Potato  Diseases  and  their  Remedies.    Vermont  Agl. 

Exp.  Sta.  Built.  72 :    1-32.    1899. 
JONES,  L.  R.,  and  GROUT,  A.  J.    Notes  on  Two  Species  of  Alternaria.    Built. 

Torrey  Bot.  Club  24:  254-258.    1897. 

STEWART,  F.  C,  EUSTACE,  H.  J.,  and  SIRRINE,  F.  A.    Potato  Spraying  Ex- 
periments in  1906.    N.  Y.  (Geneva)  Agl.  Exp.  Sta.  Built.  279:    155-229. 

1906. 
STURGIS,  W.  C.    Notes  on  "  Early  Blight "  of  Potatoes.    Conn.  Agl.  Exp.  Sta. 

Rept.  18 :   127-135.    1894. 

Habitat  relations.  The  fungus  causing  the  early  blight  of 
potatoes  was  described  in  1882.  In  1891  it  was  recorded  as  of 
economic  importance  in  the  United  States,  but  subject  to  control. 
Since  that  time  this  fungous  disease  has  grown  constantly  in  im- 
portance, although  to  a  very  large  extent  preventable.  The  early 
blight  is  common  practically  throughout  the  United  States,  and 
it  occurs  also  in  Canada,  Europe,  Asia,  and  Australia. 

In  temperate  regions  the  leaf  blight  may  be  found  from  July  to 
the  end  of  the  growing  season,  increasing  generally  as  the  season 
advances.  It  may  be  checked,  however,  by  periods  of  unusual 
drought,  but  it  does  not  appear  to  be  easily  affected  by  lesser 
changes  in  conditions. 

This  disease  is  a  typical  leaf  blight  and  may  be  distinguished 
from  the  late  blight  already  described  and  from  such  nonparasitic 
pathological  conditions  as  tip  burns  and  sunscald  by  recognizable 
leaf  characters.  The  spots  are  brown,  circular,  or  elliptical,  and 
they  are  distinctly  marked  with  concentric  or  target-board  mark- 
ings. They  are  irregularly  distributed  over  the  leaf  surface,  al- 
though frequently  occurring  upon  the  borders  of  other  injuries 
(Fig.  136).  Through  carefully  conducted  experiments  (Jones)  it 
has  been  satisfactorily  determined  that  the  fungus  may  establish 
itself  by  truly  parasitic  means,  being  capable  of  infecting  healthy 
leaves,  provided  only  that  sufficient  moisture  is  present  to  insure 
germination  and  vigorous  growth.  Nevertheless,  the  fungus  is 


302 


FUNGOUS  DISEASES  OF  PLANTS 


encouraged  by  certain  weakening  influences,  such  as  the  age  of 
the  leaf,  the  presence  of  flea-beetle  injuries,  etc.  When  large 
spots  near  the  margins  of  the  leaves  become  confluent,  such  ex- 
tensive areas  are  affected  that  there  may  result  a  rolling  up  of  the 
edge,  which  might  be  mistaken  for  the  tip  burn,  a  disease  gener- 
ally due  to  climatic  conditions. 

The  injury  from  the  early  blight  results,  therefore,  in  an  early 
death  of  the  leaves,  as  a  result  of  which  the  vines  dry  up  and  the 
losses  to  the  growing  crop  are  often  very  considerable,  amounting 

to  as  much  as  50  per  cent.  The 
disease  is  said  to  be  more  likely 
to  begin  at  the  time  of  flowering 
and  while  the  work  of  the  plant  is 
directed  toward  the  development  of 
tubers.  This  fungus  produces  no 
rot  directly. 

This  Macrosporium  is  found  not 
only  upon  the  potato  but  also  upon 
tomatoes  and  upon  the  jimson  weed, 
(Datura  Stramonium).  There  is 
also  a  very  considerable  difference 
in  the  susceptibility  of  the  different 
varieties  of  potato,  but  at  present  no 
wholly  resistant  sorts  are  known, 
although  the  general  question  of 
the  resistance  of  potatoes  to  diseases 
is  receiving  special  attention  in  the  chief  potato-growing  regions 
of  the  world. 

The  fungus.  Within  the  tissues  the  mycelium  is  light  brown  to 
olivaceous,  and  the  conidiophores  arise  through  stomates  or  push  up 
between  the  collapsed  epidermal  cells  as  erect  or  assurgent  fruiting 
hyphae  50-90  x  8-9  /JL.  They  are  septate,  slightly  curved,  and,  as 
is  characteristic  of  this  genus,  the  conidia  are  produced  singly,  so 
far  as  observed,  upon  the  host.  The  conidia  have  been  described 
as  "obclavate,  brown,  145-370  x  16-18;*,  terminating  in  a  very 
long,  hyaline,  septate  beak  (apical  cells)  equalling  fully  one-half  the 
length  of  the  spore  (often  exceeding  this)  ;  body  of  spore  with  5  to 
10  transverse  septa,  longitudinal  septa  few  or  lacking  "  (Fig.  137). 


FIG.  136.    EARLY  BLIGHT  OF  THE 
POTATO 


FUNGI  IMPERFECTI 


303 


The  germ  tubes  arise  from  any  cell  of  the  spore,  and  it  is 
stated  that  they  may  enter  the  host  either  by  means  of  the 
stomates  or  by  directly  penetrating  the  cuticle.  This  fungus 
grows  vigorously  in  pure  cultures.  Upon  prune  agar  it  has 
been  found  (Jones)  that  the  spores  might  be  produced  as  a 
chain  of  two,  and  on  account  of  this  character  the  plant  has 
been  placed  in  the  related  genus  Alternaria.  As  is,  of  course, 
well  known,  the  step 
from  Macrosporium 
to  Alternaria  is  at 
best  a  very  slight 
one,  yet  it  should 
be  remembered  that 
these  genera  based 
upon  recognizedly 
variable  characters 
serve  at  most  for 
convenience.  The 
catenulate  method 
of  spore  production 
has  been  reported 
only  in  artificial  cul- 
tures in  this  case, 
and  it  is  possible, 
furthermore,  to  ob- 
tain for  various 


FIG.  137.   MACROSPORIUM  SOLANI :    GERMINATING 

SPORES     WITH     HYPH^E     ENTERING     STOMATA 

(After  Jones) 


fungi  in  such  cul- 
tures  in  general 
many  variations 
from  what  would  be  considered  the  normal  type  of  spore  production 
upon  the  host.  Attention  may  be  called  to  the  fact  that  cultures 
of  many  Stilbeae  yield  upon  agar  only  simple  conidiophores.  Cul- 
tures of  Fusarium  and  Glceosporium  are  also  modified  in  an  equiva- 
lent manner,  the  stromatic  development  being  usually  suppressed. 
Species  of  Cercospora  also  produce  spores  in  an  abnormal  manner. 
Upon  the  leaf  Macrosporium  may  be  accompanied  by  one  or  more 
species  of  true  Alternaria,  but  the  latter  are  saprophytic,  as  deter- 
mined by  experimental  work. 


304  FUNGOUS  DISEASES  OF  PLANTS 

Control.  Wherever  careful  spraying  experiments  have  been  made 
it  has  been  found  possible  in  ordinary  seasons  to  reduce  the  injuries 
from  the  early  blight  to  a  very  small  minimum  by  the  same  method 
which  has  been  recommended  in  case  of  the  late  blight  and  rot. 

XIV.    ONION  MOLD 
Macrosporium  Sarcinula  Berk. 

MIYABE,  K.    On  the  Life-History  of  Macrosporium  parasiticum  Thiim.    Ann. 
Bot.  3:    1-26.  pi.  i.    1889. 

This  fungus  has  long  been  associated  with  the  onion  mildew, 
and  by  some  pathologists  it  is  supposed  that  it  is  commonly  pres- 
ent on  diseased  onions  as  a  fungus  of  secondary  importance.  In 
many  cases  it  unquestionably  follows  the  Peronospora  of  this  host, 
but  in  other  cases  it  seems  to  be  the  direct  cause  of  spots  which 
may  involve  the  seed  stalks,  or  which  may  occur  upon  the  older 
leaves  and  sheaths.  It  occurs  in  Europe,  in  the  Bermudas,  in  the 
northeastern  United  States,  and  possibly  throughout  a  wider  range. 
It  is  conceivable  that  the  fungus  follows  injuries  of  one  sort  or 
another,  such  as  those  of  thrips  or  other  insects,  as  well  as  the 
effects  of  the  Peronospora,  but  it  does  not  appear  to  be  restricted  to 
plants  infested  by  the  last-mentioned  fungus.  In  the  case  of  onions 
grown  for  seed  it  is  especially  injurious,  since  the  seed  stalks  af- 
fected seldom  mature  their  product.  Miyabe  established  the  genetic 
connection  between  the  Macrosporium  of  onion  and  Pleospora  her- 
barum  (Pers.)  Rab.,  incidentally  indicating,  also,  that  the  Macrospo- 
rium agrees  with  the  saprophytic  form  described  by  Berkeley. 

XV.  MACROSPORIUM:  OTHER  SPECIES 

Occurring  upon  other  solanaceous  hosts  are  such  species  as 
Macrosporium  tomato  Cke.  and  Macrosporium  Datura  Fautr. 
Several  species  have  been  reported  upon  onions  besides  Macro- 
sporium Sarcinula  Berk,  above  discussed.  Other  species  of 
Macrosporium  besides  the  latter  have  also  been  connected  with 
species  of  Pleospora. 

Macrosporium  nigricantium  Atkinson,  Macrosporium  Tabaci- 
num  Ell.  &  Ev.,  and  Macrosporium  Iridis  C.  &  E.  are  commonly 
reported  as  leaf  spot  or  blight  fungi  of  their  respective  hosts,  cot- 
ton (Gossypium),  Iris,  and  tobacco  (Nicotiana  Tabacum). 


FUNGI  IMPERFECTI 


305 


XVI.  BLIGHT  OF  GINSENG1 
Alternaria  Panax  Whetzel 

Occurrence  and  symptoms.    The  so-called  " blight"  is  the  most 
common  and  destructive  disease  of  cultivated  ginseng.    It  occurs 


FIG.  138.   BLIGHT  OF  GINSENG:  FREQUENT  FORMS  OF  THE  DISEASE 
(Photograph  by  H.  H.  Whetzel) 

apparently  throughout  the  eastern  United  States  wherever  ginseng 
is  grown,  but  has  not  been  with  certainty  reported  west  of  the 
Mississippi.  The  disease  is  caused  by  Alternaria  Panax  Whetzel, 

1  This  account  of  the  blight  of  ginseng  was  kindly  prepared  by  Professor  H. 
H.  Whetzel,  Cornell  University. 


306  FUNGOUS  DISEASES  OF  PLANTS 

which,  in  its  general  characters,  as  regards  spores  (size,  shape,  etc.), 
is  very  much  like  the  Alternaria  Solani  producing  the  early  blight 
of  potatoes.  The  fungus  is  a  genuine  parasite,  attacking  plants 
both  young  and  old,  and  apparently  under  all  conditions,  although 
the  disease  becomes  epidemic  only  in  hot  rainy  weather. 

The  parasite  attacks  all  of  the  parts  of  the  plant  above  ground, 
but  never  affects  the  roots.  During  epidemic  periods  the  disease 
works  with  great  rapidity,  so  that  the  tops  of  plants  in  an  entire 
garden  may  be  entirely  destroyed  within  a  few  days.  The  disease 
first  makes  its  appearance  as  dead  brown  streaks  or  cankers  on 
the  stems  of  the  plants  near  the  ground.  This  is  the  primary  in- 
fection in  the  spring,  and  it  is  probably  brought  about  through 
spores  that  have  wintered  over  on  the  mulch  or  debris  on  the 
soil,  the  stems  becoming  infected  as  they  come  through  the 
ground.  This  first  stage  is  usually  overlooked  by  the  grower 
unless  it  becomes  severe  enough  to  cause  the  breaking  over 
of  the  stems,  which  sometimes  happens.  Ordinarily  the  first 
observed  appearance  of  the  disease  is  on  the  leaves,  which  show 
rather  large,  more  or  less  circular,  watery  spots.  The  tissue  is 
killed  outright  in  those  spots  and  later  becomes  dry  and  papery 
with  a  brown  or  yellowish  center.  Under  favorable  weather  con- 
ditions .these  spots  spread  and  coalesce,  readily  killing  the  leaves 
and  the  entire  top  of  the  plant  (Figs.  138,  139),  so  that  a  badly 
blighted  plantation  looks  as  if  it  had  been  drenched  with  scalding 
water.  If  the  berries  set  before  the  blight  has  become  destructive, 
they  may  be  attacked  and  blasted,  turning  brown  and  dropping  off 
before  they  can  ripen. 

The  fungus.  The  conidia  or  spores  of  the  parasite  are  pro- 
duced in  great  abundance  on  all  parts  of  the  affected  plants,  but 
particularly  so  on  the  stems  and  blasted  berries.  No  perfect  or 
winter  stage  has  been  discovered  for  the  fungus,  but  the  fact  that 
the  spores  will  germinate  after  remaining  in  the  laboratory  dry  for 
three  months  indicates  that  the  conidia  of  the  fungus  are  prob- 
ably carried  over  winter  on  the  mulch  or  debris  on  the  beds.  It 
grows  very  readily  as  a  saprophyte,  and  may  pass  the  winter 
growing  on  the  dead  stems  and  mulch  on  the  bed.  The  fungus 
makes  its  first  appearance  on  the  stems  early  in  the  spring,  shortly 
after  they  are  up,  but  the  disease  does  not  become  destructive 


FUNGI  IMPERFECTI 


307 


usually  before  the  middle  or  latter  part  of  the  summer  ;  so  that  the 
tops  are  not  often  killed  before  the  middle  of  July  or  the  first  of 
August  in  New  York.  The  parasite  does  not  pass  down  into  the 
root  nor  does  it  induce  rot  of  any  kind  in  the  roots.  The  general 
effect  on  the  root  of  the  plant  is  to  reduce  its  growth,  and  proba- 
bly where  the  blight  continues  year  after  year  the  root  will  be  so 
weakened  that  it  will  become  subject  to  soil  rots  of  various  kinds. 


FIG.  139.   BLIGHT  OF  GINSENG:  A  SEVERE  ATTACK  BEGINNING  WHEN  THE 
PLANTS  WERE  YOUNG.    (Photograph  by  H.  H.  Whetzel) 

Control.  It  has  been  clearly  demonstrated  that  this  disease  may 
be  controlled  by  thorough  spraying  with  Bordeaux  mixture.  The 
application  should  begin  early  in  the  spring,  as  soon  as  the  plants 
come  through  the  ground,  and  should  be  kept  up  throughout  the 
season  every  ten  days  or  two  weeks.  It  is  particularly  necessary 
to  spray  the  young  plants  frequently  when  they  are  coming  through 
the  soil  in  order  to  protect  them  from  the  primary  infection.  It 
has  been  shown  that  ginseng  is  able  to  stand  a  very  strong  solution 


308  FUNGOUS  DISEASES  OF  PLANTS 

of  Bordeaux  mixture,  so  that  the  ordinary  strength  may  be  used 
without  causing  any  trouble.  In  the  case  of  the  early  sprayings 
in  the  spring  when  there  is  apt  to  be  cold  weather,  it  has  been 
found  that  plants  will  sometimes  be  injured  by  the  Bordeaux.  If 
care  is  taken  not  to  apply  the  mixture  just  before  a  hard  freeze, 
little  trouble  will  result. 

Alternaria  Violae  Gall.  &  Dorsett 1  produces  a  leaf  spot  of  violets 
in  the  greenhouse,  particularly  when  the  houses  are  not  well  regu- 
lated with  respect  to  dryness  or  moisture  of  the  air,  heat  and  cold, 


FIG.  140.   LEAF  SPOT  OF  BEETS;  A  FIELD  OF  SUGAR  BEETS  BADLY  DISEASED 

or  when  the  stock  is  not  in  condition  for  vigorous  growth.  The 
old  spots,  as  in  the  case  of  most  violet  leaf  diseases,  are  white, 
although  at  the  outset  the  spot  is  dark,  and  on  the  stem  (which  is 
sometimes  affected)  the  darkened  areas  are  often  persistent. 

Alternaria  Brassicae  (Berk.)  Sacc.  This  species  is  not  uncom- 
mon upon  cabbage  and  horse  radish  in  Europe  and  America.  It 
produces  brown  spots  with  concentric  markings. 

1  Dorsett,  P.  H.  Spot  Disease  of  the  Violet.  Div.  Veg.  Phys.  and  Path.,  U.  S. 
Dept.  Agl.  Built  23  :  1-16.  pis.  7-7.  1900. 


FUNGI  IMPERFECTI 


309 


XVII.    LEAF  SPOT  OF  BEETS 
Cercospora  Heticola  Sacc. 

DUGGAR,   B.  M.    Leaf  Spot  of  the  Beet.    Cornell  Agl.  Exp.  Sta.  Built.  163 : 

352-359-  figs.56-61-    l898- 

PAMMEL,  L.  H.    Spot  Disease  of  Beets.    Iowa  Agl.  Exp.  Sta.  Built.  15 :  238- 
243.    1891. 

Habitat  relations.  The  beet  leaf  spot  is  widely  distributed.  Both 
in  Europe  and  America  it  is  a  fungus  of  common  occurrence,  and 
it  is  believed  to  be  more  or 
less  prevalent  wherever 
beets  are  grown  even  to  a 
limited  extent.  The  red 
garden  beet  is  seldom 
wholly  free  from  this 
fungus,  although  many 
varieties  are  apparently  so 
resistant  that  the  disease 
is  not  an  important  one 
in  garden  or  truck  work. 
Much  damage  may  be 
done  to  sugar  beets  in 
any  region  where  summer 
rains  or  heavy  dews  are 
prevalent.  Spanish  and 
Swiss  chard  are  seldom 
affected  to  an  injurious 
extent. 

The  leaf  spots  are  at 
first  very  small  brown 
flecks  with  reddish-purple 
borders.  As  soon  as  the 
spots  attain  a  diameter  of  \  inch  or  more  they  become  ashen  gray 
at  the  center,  the  border  remaining  as  before  so  long  as  the  blade 
is  green.  The  spots  are  distributed  over  the  leaf  surface  (Fig.  141), 
and  they  may  become  so  numerous  as  to  cover  a  large  portion  of 
the  surface,  yet  with  no  general  discoloration  of  the  blade.  In 
time,  however,  the  leaves  blacken  and  dry  up  gradually  from  tip 
to  base.  As  the  leaves  become  parched  and  dry  they  stand  more 


FIG.  141.   LEAF  SPOT  OF  BEETS 


3io 


FUNGOUS  DISEASES  OF  PLANTS 


FIG.  142.    EFFECTS  OF  THE  LEAF-SPOT 
FUNGUS:  PROLONGED  CROWN 


nearly  upright,  although  some- 
what curled  or  rolled,  present- 
ing a  characteristic  appearance 
in  the  field. 

Since  the  outer  leaves  are 
the  first  to  succumb,  the  plant 
continues  to  develop  new  leaves 
from  the  bud,  and  the  crown 
may  thus  become  considerably 
elongated  (Fig.  142),  at  a  seri- 
ous sacrifice  to  root  develop- 
ment, and  probably  at  great  loss 
to  the  sugar  content. 

It  has  been  stated  by  German 
observers  that  the  leaf -spot  fun- 
gus may  also  be  found  upon  the 
bracts,  peduncles,  and  even  upon 
the  seed  pods.  It  is  therefore 
thought  that  the  fungus  may  be  spread  with  the  seed. 

The  fungus.  When  the  leaf  spots 
appear  gray  at  the  centers  one  may 
be  sure  of  finding  the  conidiophores 
and  conidia  of  the  fungus  in  abun- 
dance. The  former  arise  in  small 
clusters,  apparently  through  the 
stomates  at  first.  The  base  of  the 
cluster  is  usually  a  few-celled  stroma. 
The  conidiophores  are  flavous,  and 
ordinarily  35-55x4-5/4.  The  co- 
nidia are  produced  at  the  apices,  and 
then  by  further  growth  of  the  conid- 
iophores, slightly  towards  one  side, 
noticeable  geniculations  are  left,  and 
the  conidiophores  are  therefore  flex- 
uous.  The  conidia  are  obclavate  to 
needle-shaped,  hyaline,  many-celled, 

75-200  X  3.5-4.5  A*  (^g.   M3).      H      FIG.  143.   CRRCOSPORA  BETICOLA: 
produced  under  very  moist  conditions,      CONIDIOPHORES  AND  CONIDIA 


FUNGI   IMPERFECTI 


as  in  a  moist  chamber,  the  length  mentioned  may  be  considerably 
exceeded.  After  the  death  of  a  leaf,  spores  may  be  produced  over 
the  entire  surface.  Spores  found  upon  old  leaves  in  the  field  five 
months  after  the  beets  were  harvested  were  able  to  germinate. 

The  fresh  spores  germinate  readily  in  ordinary  nutrient  media, 
and  pure  cultures  may  be  obtained  by  the  poured  plate  method. 
After  a  growth  of  a  few  days  the  colonies  show  up  well.  The  sub- 
merged mycelium  develops  in  agar  as  a  dense  olivaceous  colony, 
the  new  growth  lighter  in  appearance,  forming  an  outer  border. 
The  aerial  growth  of  the  colonies  is  finally  grayish  green.  On 
bean  pods  a  copious  development  of  mycelium  occurs,  but  such 
cultures  maintained 
for  two  years  gave 
no  production  of 
conidia.  Abnormal 
conidia  may,  how- 
ever, be  developed 
on  this  medium 
from  other  species 
of  Cercospora  in  cul- 
ture. Aerial  hyphae 
show  a  tendency  to 
adhere  together  in 
slight  strands  or 
clusters,  and  the 
small  branches  sug- 
gest an  attempt  at  spore  production  (Fig.  144,  aerial).  The  im- 
mersed mycelium  is  very  irregular,  with  many  swollen  cells  and 
peculiar  branches  (Fig.  144).  I  have  grown  about  twenty  spe- 
cies of  Cercospora  in  pure  cultures,  but  in  no  case  has  any  evi- 
dence or  clue  been  obtained  as  to  the  possible  connection  with 
a  perithecial  form. 

Control.  Such  experiments  as  have  been  made  indicate  that 
this  disease  can  be  controlled,  where  necessary,  by  Bordeaux 
mixture.  Since  the  conidia  may  retain  their  vitality  until  late 
winter,  it  is  probable  that  many  are  able  to  germinate  after  the 
seed  are  sown  in  the  late  spring ;  early  spraying  is  therefore 
important. 


FIG.  144.   MYCELIUM  OF  CERCOSPORA  IN  CULTURE: 
AERIAL  AND  SUBMERGED  FORMS 


3I2 


FUNGOUS  DISEASES  OF  PLANTS 


XVIII.    EARLY  BLIGHT  OF  CELERY 
Cercospora  Apii  Fr. 

ATKINSON,  GEO.  F.    Note  on  the  Cercospora  of  Celery  Blight.    Cornell  Agl. 

Exp.  Sta.  Built.  48:  314-316.  fig.  5.    1892. 
DUGGAR,  B.  M.    Early  Blight  of  Celery.    Cornell  Agl.  Exp.  Sta.  Built.  132 : 

201-206.  figs.  48-50.    1897. 
STURGIS,  W.  C.    On  the  Prevention  of  Leaf-Blight  and  Leaf-Spot  of  Celery. 

Conn.  Agl.  Exp.  Sta.  Rept.  21:  167-171.    1897. 
U.  S.  Dept.  Agl.  Rept.  (1886):  117-120.- 


Habitat  relations.  Cercospora  Apii  is  the  cause  of  the  chief 
disease  of  celery,  beginning  early  in  the  season.  It  is  common  in 

the  Atlantic  states  and  well  known  in 
the  Mississippi  Valley.  It  is  also  a 
serious  pest  in  Europe.  In  the  early 
stages  of  the  disease  there  is  a  well- 
defined  spot  with  slightly  raised  bor- 
der ;  but  when  the  spots  become 
numerous  on  a  leaf,  the  latter  begins 
to  turn  yellow,  and  subsequently  the 
fungus  develops  abundantly  its  conid- 
iophores  in  indefinite  areas,  thus  giv- 
ing the  characteristic  ashen  or  velvety 
spots  of  indiscriminate  form.  When 
a  leaf  becomes  seriously  injured  it 
wilts  and  dries.  The  conidia  are  then 
produced  in  quantity  over  the  whole 
surface,  particularly  during  muggy 
days ;  thus  the  dead  leaves  increase 
many  times  the  chances  of  further  in- 
fection. This  disease  does  not  usually 
appear  late  in  the  season,  being  fre- 
quently followed  by  the  late  blight 
(Septoria  Petroselini  var.  Apii}  with  which  it  has  no  genetic  con- 
nection. This  fungus  also  occurs  on  cultivated  and  wild  parsnip 
(Pastinaca  sativd)  and  other  related  plants. 

The  fungus.  The  conidiophores  and  conidia  of  this  Cercospora 
are  in  no  way  particularly  characteristic.  The  conidiophores  and 
spores  are  variable  in  size,  depending  upon  the  conditions  under 


FIG.  145.  CERCOSPORA  APII:  AB- 
NORMAL FRUITING  IN  CULTURE 


FUNGI  IMPERFECTI  313 

which  produced ;  the  former  measure  in  extreme  cases  50-150  x 
4-5  /z,  and  the  spores,  50-280  x  4-5 /*.  They  attain  the  maximum 
size  with  both  high  humidity  and  temperature.  The  spores  retain 
their  vitality  for  many  months  at  least.  Pure  cultures  of  this  fun- 
gus may  be  readily  secured  by  the  poured  plate  method,  and  the 
mycelium  grows  well  upon  bean  stems  and  other  media.  In  such 
cultures  the  conidiophores  are  most  peculiar.  They  may  attain  a 
length  of  a  millimeter  (Fig.  145).  Conidia  may  be  produced  and 
abscised  for  a  time,  leaving  the  customary  geniculation ;  then 
when  the  hyphae  are  longer,  conidia-like  branches  arise,  which  re- 
main attached,  and  eventually  serve  as  true  branches  of  perma- 
nent hyphae.  The  mycelium,  like  that  of  the  other  Cercosporae,  is 
olivaceous ;  but  the  colonies  show  minor  peculiarities  distinguish- 
ing them  from  other  species  which  have  been  thus  cultivated. 

Control.  This  fungus  may  be  controlled  by  early  spraying  with 
Bordeaux  mixture,  5-5-50  formula,  or  by  repeated  applications  of 
ammoniacal  copper  carbonate.  It  is  also  claimed  that  partial  shade, 
usually  affording  more  equable  temperature  and  moisture  relations 
for  the  host,  enable  the  plant  to  resist  the  fungus  to  a  very  large 
degree. 

XIX.    LEAF  BLIGHT  OF  COTTON 

Cercospora  Gossypina  Cke. 

ATKINSON,  GEO.  F.  Sphaerella  Gossypina,  n.  sp.  the  Perfect  Stage  of  Cerco- 
spora Gossypina  Cooke.  Built.  Torrey  Bot.  Club.  18:  300-301.  1891. 

ATKINSON,  GEO.  F.  Cotton  Leaf  Blight.  Ala.  Agl.  Exp.  Sta.  Built.  41 :  58- 
61.  fig.  19.  1892. 

SCRIBNER,  F.  L.  Cotton  Leaf  Blight.  U.  S.  Dept.  Agl.  Kept.  (1887):  355- 
357.  pi.  4. 

This  fungus  produces  a  leaf  blight  of  cotton.  It  is  more  com- 
mon on  the  less  vigorous  or  old  leaves,  and  it  is  generally  reported 
as  prevalent  when  for  any  reason  the  vitality  of  the  plant  is  lowered. 
The  spots  are  at  first  small  and  red,  later  becoming  pale  and  finally 
brown  at  the  centers.  They  are  generally  1-5  mm.  in  diameter, 
but  sometimes  confluent  and  extensive.  Conidiophores  and  conidia 
are  at  first  produced  only  in  the  central  area  of  these  spots,  but  on 
leaves  the  vitality  of  which  is  largely  lost  the  fungus  may  appear 
over  large  areas.  Atkinson  considers  this  fungus  a  conidial  stage 
of  Sphcerella  Gossypina  Atk. 


FUNGOUS   DISEASES   OF  PLANTS 


FIG.  146.    CERCOSPORA  GOSSYPINA:  AN 
ISOLATION  CULTURE 


XX.  CERCOSPORA:   OTHER  SPECIES 

Parallel    cultures    on    diverse   culture    media   of  a    number  of 
species  on  related  hosts  would  be  of  special  interest.    As  in  the 

case  of  Phyllosticta,  subse- 
quently discussed,  numerous 
leaf  spots  are  produced  by 
members  of  this  genus  Cerco- 
spora.  Very  few  cross  inocula- 
tions have  been  made,  and  little 
is  really  known  concerning  the 
limitations  of  species.  When 
the  host  plants  are  different, 
minor  variations  in  the  size, 
color,  septation,  etc.,  of  spores 
and  conidiophores,  or  in  the 
macroscopic  appearances  of 
spots,  are  generally  employed 
in  distinguishing  species. 
Among  many  other  species  the  following  upon  important  hosts 
may  be  mentioned. 

Cercospora  Viticola  Sacc.  This  fungus  produces  a  spot  known 
as  grape  leaf  blight.  It  has  not  been  productive  of  serious  damage 
except  during  unusually  moist  seasons.  The 
spots  are  first  evident  on  the  lower  surface  of 
the  leaf,  and  it  is  also  upon  this  surface  that 
the  conidiophores  are  developed.  Upon  Am- 
pelopsis  quinquefolia  a  Cercospora  is  more 
commonly  found,  but  apparently  no  com- 
parative study  of  these  different  forms  has 
been  made. 

Cercospora  circumscissa  Sacc.  is  one  of  the 
shot-hole-producing  leaf  fungi  of  the  genus 
Prunus.  It  occurs  on  some  of  the  native 
American  as  well  as  cultivated  species  of 
plums  and  cherries  (Fig.  147)  and  on  the  nec- 
tarine and  peach.  It  is,  however,  not  so  important  from  a  patho- 
logical point  of  view  upon  most  of  these  hosts  as  Cylindrosporium 


FIG.  147.  CERCOSPORA 
CIRCUMSCISSA:  SPOTS  ON 
ALMOND.  (After  Pierce) 


FUNGI  IMPERFECTI 


315 


Padi,  but  it  is  important  as  an  almond  tree  disease1  in  California 
and  elsewhere. 

Cercospora  Nicotianae  E.  &  E.  The  more  commonly  observed 
leaf  spot  or  frog  eye  of  the  tobacco  has  been  reported  from  many 
tobacco-growing  regions,  but  does  not  appear  to  be  a  disease  of 


FIG.  148.    CERCOSPORA  CIRCUMSCISSA.    (After  Pierce) 
a,  tuberculate  stroma ;  b,  conidiophores  and  conidia 

any  great  importance,  and  doubtless  many  different  fungi  are  con- 
cerned in  the  production  of  spots  more  or  less  similar  which  have 
been  reported  in  nonscientific  literature. 

Cercospora  Violae  Sacc.,  producing  white  spots  on  leaves  of  the 
violet  in  the  spring,  is  common  in  coldframe  or  garden  culture. 

Cercospora  Diospyri  Thiim.  is  of  common  occurrence  in  the  south- 
ern states  on  leaves  and  fruit  of  persimmon  (Diospyros  virginiand). 

Cercospora  sordida  Sacc.  is  the  most  important  disease-produc- 
ing fungus  of  the  trumpet  creeper  (Tecoma  radicans\  in  the 
United  States.  Pale  spots  are  produced  on  the  leaves,  and  defoli- 
ation of  the  host  often  results  by  midsummer. 

1  Pierce,  N.  B.  A  Disease  of  Almond  Trees.  Journ.  Myc.  7  :  66-77.  ph.  11-14. 
1892. 


3i6 


FUNGOUS  DISEASES  OF  PLANTS 


XXI.    SPONGY  DRY  ROT  FUNGUS  OF  APPLE 
Volutetta  fructi  Stevens  &  Hall 

STEVENS,  F.  L.,  and  HALL,  J.  G.    The  Volutella  Rot.     N.  C.  Agl.  Exp.  Sta. 
Built.  196:  41-48.    1907. 

The  rot  of  apples  produced  by  this  fungus  has  been  reported 
from  North  Carolina  in  particular,  although  the  disease  has  also 
been  found  upon  apples  from  other  states.  The  disease  usually 
begins  as  a  small  spot  which  gradually  increases  to  include  the 
whole  fruit.  A  characteristic  of  the  injury 
is  found  in  the  coal  black  color  of  the  older 
portions  of  the  spot. 

The  effect  upon  the  tissues  is  to  produce  a 
rather  spongy  dryness,  and  the  whole  affected 
tissue  is  penetrated  by  a  much-branched, 
closely  septate  mycelium,  most  abundant, 
however,  close  to  the  cuticle  ;  in  fact,  a  sub- 
cuticular,  hyaline  stroma  is  formed,  which 
in  places  eventually  becomes  palisade  in 
arrangement.  From  these  stromatic  forma- 
tions arise  a  mass  of  erect  tuberculate  hyphae 
bearing  numerous  spores.  Setae  are  present, 
originating  in  the  midst  of  the  sporogenous 
hyphae,  each  seta  produced  from  the  tip  of  a 
single  hypha.  These  vary  from  I  oo  to  400  /JL 
in  length,  and  may  be  from  5  to  8  /n  in 
diameter  near  the  base.  The  conidiophores  arise  much  higher  up, 
and  they  are  relatively  short,  simple,  fertile  hyphae,  each  abscising 
many  oblong-fusoid  to  falcate-fusoidal  spores  (Fig.  149). 

This  fungus  grows  readily  in  culture  upon  ordinary  nutrient 
media,  and  the  color  of  the  mycelium  varies  greatly,  being  almost 
hyaline  on  some  and  practically  black  on  other  media.  Upon  the 
host  the  sporodochia  occur  in  concentric  circles,  and  these  are 
commonly  subcuticular  at  first,  becoming  erumpent.  The  conidia 
are  continuous,  hyaline  to  olivaceous,  and  about  the  length  of  the 
normal  conidiophores.  The  fungus  has  only  been  found  on  the 
apple,  to  which  it  is  probably  confined.  The  disease  is  easily  dis- 
tinguished from  the  fruit  spot. 


FlG.       149.        VOLUTP.LLA 

FRUCTI.  (After  Stevens) 


FUNGI  IMPERFECTI  317 

Volutella  Dianthi  Atk.1  is  not  uncommon  on  carnations  in 
moist  situations.  It  attacks  particularly  those  parts  more  or  less 
in  contact  with  a  damp  soil.  In  favorable  conditions  the  fungus 
may  spread  with  great  rapidity  and  so  weaken  the  plant  as  to 
materially  inhibit  the  production  of  flowers.  It  may,  however, 
be  more  severe  on  the  cutting  bench,  especially  when  sufficient 
ventilation  or  drainage  is  not  provided. 

XXII.    DRY  ROT  OF  POTATOES 
Fusarium  oxysporum  Schl. 

SMITH,  ERW.  F.,  and  SWINGLE,  D.  B.  The  Dry  Rot  of  Potatoes  due  to  Fu- 
sarium Oxysporum.  Bureau  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  55  :  1-64. 
pis.  1-8.  1904. 

Much  confusion  has  prevailed  concerning  the  organisms  caus- 
ing some  of  the  diseases  of  potatoes  both  in  this  country  and  in 
Europe.  Various  types  of  potato  rot  have  been  ascribed  to  a  large 
number  of  different  organisms,  oftentimes  upon  insufficient  proof, 
or  sometimes  merely  from  a  single  observation  indicating  the  as- 
sociation therewith  of  a  particular  fungus. 

It  is  very  probable  that  many  of  the  diseases  described  under 
the  name  of  dry  rot,  end  rot,  bundle  blighting,  etc.,  are  due  to  the 
fungus  here  discussed.  Smith  and  Swingle  have,  by  careful  cul- 
tural and  inoculation  experiments,  demonstrated  the  causal  con- 
nection of  a  Fusarium  with  these  types  of  disease,  and  they  have 
taken  as  the  name  of  the  species  here  discussed  the  earliest  de- 
scribed species  of  Fusarium  associated  with  such  diseases,  namely, 
the  one  given  above,  and  they  would  regard  as  probably  synony- 
mous with  this  species  half  a  dozen  or  more  names  subsequently 
applied  to  fungi  described  as  producing  more  or  less  similar  types 
of  disease  in  the  potato. 

Symptoms.  The  effect  of  this  fungus  upon  the  host  is  prima- 
rily to  produce  a  wilt,  although  previous  to  the  wilting  the  affected 
plants  have  a  tendency  to  lie  prostrate  on  account  of  the  gradual 
destruction  of  the  root  system  by  the  fungus.  The  fungus  ap- 
parently gains  entrance  through  the  roots,  and  from  these  parts 

1  Halsted,  B.  D.  The  Carnation  Anthracnose.  N.  J.  Agl.  Exp.  Sta,  Kept.  14; 
385-386.  1893. 


FUNGOUS  DISEASES  OF  PLANTS 


spreads  to  the  stem  and  leaves.  Entrance  to  the  tubers  is  gained, 
therefore,  as  a  rule,  through  the  stems  upon  which  they  are 
borne.  The  vascular  system  of  the  host  plant  is  discolored,  al- 
though frequently  the  tubers  are  not  seriously  injured  externally 
until  after  they  are  gathered.  In  storage,  however,  the  fungus 
progresses  rapidly,  blackening  the  vascular  ring.  At  this  stage 
the  disease  is  only  made  apparent  in  the  tubers  by  cutting  them 
crosswise  ;  still  it  may  be  so  serious  as  to  render  them  unavailable 
for  table  purposes.  Later  on  there  may  be  considerable  drying  of 
the  tubers,  or  soft  rots  due  to  secondary  organisms  may  ensue. 

The  fungus. 
The  mycelium 
produces  micro- 
conidiaand  macro- 
conidia  (Fig.  150) 
abundantly  in  arti- 
ficial cultures,  also 
some  chlamydo- 
spores.  On  boiled 
potatoes  small 
greenish  sclerotia 
are  developed,  but 
no  ascogenous 
stage  has  thus  far 
been  connected 
with  this  species. 
Control.  This  fungus  lives  apparently  for  a  considerable  time 
in  the  soil,  and  a  rotation  of  crops  is  essential  whenever  it  be- 
comes of  serious  importance.  Again,  the  use  of  pure  seed  only 
should  be  allowed.  If  necessary,  inspect  by  cutting  a  large  num- 
ber of  the  tubers  which  are  to  be  used  for  this  purpose.  All 
diseased  and  discarded  tubers  should  be  burned  and  not  returned 
to  the  land.  Seed  tubers  which  may  have  come  in  contact  with 
conidia  should  be  treated  as  for  potato  scab. 

The  sleepy  disease  of  tomatoes  which  has  been  attributed  to 
Fusarium  Lycopersici  Sacc.  may  also  be  produced  by  the  fungus 
above  described,  although  this  point  has  not  been  demonstrated 
experimentally. 


FIG.  150.   FUSARIUM  OXYSPORUM :  MYCELIUM,  CONIDIA, 
AND  CHLAMYDOSPORE 


FUNGI  IMPERFECTI 


319 


XXIII.    FLAX  WILT 
Pusarium  Lini  Bolley 

BOLLEY,  H.  L.    Flax  Wilt  and  Flax  Sick  Soil.    N.  D.  Agl.  Exp.  Sta.  Built. 
50:   27-60. 

This  important  flax  disease,  which  is  reported  as  particularly 
destructive  in  North  Dakota,  seems  to  be  characterized  by  symp- 
toms similar  to  many  other  diseases  caused  by  species  of  Fusa- 
rium.  Affected  plants  may  be  killed  in  the  seedling  stage,  or 
they  may  wilt  and  die  at  any  time  during  the  growing  period. 

The  fungus  has  been  found  to  be  ordinarily  very  abundant  in 
soils  in  which  flax  has  been  grown  several  successive  years,  and 
it  is  considered  to  be  the 
chief  cause  of  the  failure 
of  flax  upon  land  where 
flax  has  previously  been 
grown.  In  fact,  Bolley 
points  to  this  fungus  as 
the  cause  of  flax-sick  soil. 
It  would  seem  to  be  doubt- 
ful, however,  if  the  action 
of  this  fungus  would  ex- 
plain all  the  peculiar  rela- 
tions of  flax  to  the  soil 
upon  which  it  has  been 
grown.  The  fungus  pro- 
duces an  abundance  of  conidia  which  are  typically  somewhat 
curved,  4-celled,  and  prompt  to  germinate.  No  perfect  stage  of 
this  organism  has  been  found.  It  is  believed  that  the  old  straw, 
stubble,  etc.,  of  diseased  stalks  harbor  the  fungus,  and  that  since 
the  fungus  is  in  nature,  perhaps,  more  particularly  a  saprophyte, 
there  is  ordinarily  abundant  opportunity  for^  it  to  be  carried  over 
from  one  year  to  the  next. 

Control.  Control  consists  of  seed  treatment ;  yet  in  this  con- 
nection it  should  be  said  that  the  seed  of  flax  are  very  readily 
injured  by  treatment  even  with  water,  and  therefore  much  caution 
is  needed  to  prevent  injury  to  the  seed.  It  is  advised  to  sprinkle 
the  seed  with  a  formalin  solution,  using  formalin  at  the  rate  of 


FIG.  151.   CHINA  ASTERS  DWARFED  AND 
KILLED  BY  FUSARIUM 


320 


FUNGOUS  DISEASES  OF  PLANTS 


about  2  ounces  to  each  5  gallons  of  water.  The  treatment  should 
be  given  while  the  seed  are  spread  out  on  a  floor  or  canvas,  and  as 
the  seed  are  sprinkled  the  grain  must  be  handled  continuously  with  a 
shovel  or  rake,  so  that  they  may  be  moistened,  but  not  wet,  through- 
out. Subsequently,  they  should  be  handled  until  dry.  Preceding 
this  treatment,  moreover,  the  seed  should  be  thoroughly  cleaned  in 
the  fanning  mill.  All  straw,  chaff,  and  other  refuse  from  the  pre- 
vious crop  should  be  taken  from  the  land,  as  far  as  practicable. 


XXIV.  FUSARIUM:  OTHER  SPECIES 

It  is  apparent  that  the  old  view,   which  held  species  of  the 
genus  F'usarium  to  be  largely  saprophytic,  must  be  considerably 

modified.  It  is  a  genus 
which  will  well  reward  the 
student  who  may  devote 
himself  to  it. 

Reed1  has  recently  de- 
scribed a  disease  of  the 
ginseng  caused  by  a  spe- 
cies of  Fusarium.  The 
cultural  characters  of  the 
organism  isolated  led  him 
to  believe  that  it  is  at  least 
the  same  species  as  that 
producing  the  wilt  of  cot- 
ton and  other  plants,  and 
although  the  ascigerous 
stage  was  not  found,  he  re- 
ferred it  to  Neocosmospora 
vasinfecta  (Atk.)  Erw. 
Smith. 

A  destructive  stem  blight 
FIG.  iC2.   CHINA  ASTER  AFFECTED  BY  _.  ,        .     . 

FUSAR.UM  (F'gS-    '5  I,    152)    of    the 

China  aster,    Callistephus 
hortensis  Cass.,  has  been  attributed  to  a  Fusarium,  but  a  complete 


1  Reed,  H.  S.  Diseases  of  the  Cultivated  Ginseng,  Missouri  Agl.  Exp.  Sta. 
Built.  69  :  43-65.  figs.  1-8.    1905. 


FUNGI  IMPERFECTI 


321 


study  of  the  disease  does  not 
appear  to  have  been  reported. 
The  carnation  stem  wilt,1' 2 
or  rosette,  is  occasionally 
important  both  in  the 
greenhouse  and  garden.  As 
in  the  case  of  the  cotton 
wilt  and  other  similar  dis- 
eases, the  fungus  seems  to 
gain  entrance  through  the 
root  system,  and  its  path 
of  attack  is  mainly  the 
tracheal  tissues.  Steriliza- 
tion of  the  soil  seems  to 
be  the  only  effective  means 
of  prevention. 


FIG.  153.   FUSARIUM  ON  CARNATION 

ROSETTE  EFFECT 
(Photograph  by  Geo.  F.  Atkinson) 


XXV.    ROOT  ROT  OF  THE  VINE 
Dematophora  necatrix  Hartig 

HARTIG,  R.  Rhizomorpha  (Dematophora)  necatrix  n.  sp.  Unters.  a.  dem 
forstbot.  Institut  zu  Miinchen.  3  :  94-141. //J.  6,  7.  1883. 

VIALA,  P.  Monographic  du  Pourridie'  des  Vignes  et  des  arbres  fruitiers.  1 1 8 
pp.  j  pis.  1892. 

VIALA,  P.    Pourridie'.    Maladies  de  la  Vigne.    248-329.   figs.  74-125.    1893. 

There  is  said  to  exist  throughout  a  large  part  of  Europe  and 
the  United  States  a  root  disease  of  the  grapevine  due  to  the  fun- 
gus given  above.  In  recent  years  investigations  in  the  United 
States  have  apparently  failed  to  develop  any  special  disease  to 
which  the  characteristics  usually  associated  with  Dematophora 
would  apply.  Moreover,  the  studies  in  Europe,  unfortunately, 
develop  much  conflicting  evidence.  It  would,  therefore,  seem 
necessary  before  forming  any  final  judgment  in  this  matter  to 
await  further  critical  study.  It  is  quite  possible  that  several  inde- 
pendent diseases  are  here  confused.  The  fungus  is  generally  de- 
scribed as  having  several  types  of  mycelium.  It  is  stated  that 

1  Atkinson,  Geo.  F.    Carnation  Diseases.    Amer.  Florist  8  :  720-728.    1893. 

2  Sturgis,  W.  C.    Preliminary  Investigations  on  a  Disease  of  Carnation.    Conn. 
(New  Haven)  Agl.  Exp.  Sta.  Kept.  21 :   175-181.    1897. 


322  FUNGOUS  DISEASES  OF  PLANTS 

directly  associated  with  the  roots,  the  mycelium  may  be  at  first  almost 
white  and  flocculent,  later  becoming  brownish-red.  A  rhizomor- 
phic  stage  is  also  developed,  which  is  clearly  distinguishable  from 
that  of  Agaricus  melleus.  This  may  be  in  contact  with  the  roots, 
often  beneath  the  bark,  but  it  also  provides  for  the  spread  of  the 
fungus  through  the  soil.  It  may  give  rise  to  a  filamentous  my- 
celium in  the  soil.  According  to  Hartig  tuberculate  sclerotia  are 
often  produced  from  the  strand  beneath  the  bark  or  from  the  gen- 
eral mycelium  upon  the  dead  vines.  From  the  sclerotia  as  well  as 
from  any  superficial  mycelium  there  may  arise  clusters  of  hyphae 
(conidiophores)  bearing  minute,  simple,  hyaline  conidia.  Pycnidial 
and  perithecial  stages  have  been  described.  Hartig  was  convinced 
that  he  had  clearly  established  the  parasitism  of  Dematophora  and 
that  it  might  be  considered  a  fungus  of  much  practical  signifi- 
cance, not  only  with  respect  to  viticulture,  but  also  important  in 
connection  with  the  fruit  interests  generally,  for  the  fungus  is 
reported  as  of  serious  consequence  to  fruit  orchards  throughout 
southern  Europe.  Diverse  opinions  prevail  with  respect  to  a  per- 
fect stage  of  this  organism. 

XXVI.    ANTHRACNOSE  OF  BEAN 
Colletotrichum  Lindemuthianum  (Sacc.  &  Magn.)  Scribner 

BEACH,  S.  A.    Bean  Anthracnose  and  its  Treatment.    N.  Y.  (Geneva)  Agl. 

Exp.  Sta.  Kept.  11 :  531-552.  figs.  1-7.    1892. 
FULTON,  H.  R.    Bean  Diseases.    Anthracnose  or  Pod  Spot.    La.  Agl.  Exp. 

Sta.  Built.  101:  9-13.    1908. 
WHETZEL,  H.  H.    Some  Diseases  of  Beans.    Cornell  Univ.  Agl.  Exp.  Sta. 

Built.  239:   198-214.  Jigs.  99-115.    1906. 
WHETZEL,  H.  H.    Bean  Anthracnose.    Cornell  Univ.  Agl.  Exp.  Sta.  Built. 

255:  431-447.  figs.  217-222.    1908. 

Distribution  and  host  relations.  The  bean  anthracnose  or  pod 
spot  ranks  with  the  blight  in  importance.  It  is  widely  distributed 
throughout  the  limits  of  bean  culture,  and  it  occurs  both  upon 
field  and  garden  varieties.  There  are  probably  some  differences 
in  the  resistance  of  the  various  varieties  to  the  attacks  of  the 
fungus,  but  there  is  as  yet  no  experimental  evidence  to  show 
that  immune  varieties  exist.  It  is  probable  that  many  of  the 
so-called  "  rust-proof "  sorts  indicate  merely  that  the  seed  were 
selected,  through  a  generation  or  two,  from  fields  which  showed 


FUNGI  IMPERFECTI 


323 


no  anthracnose.    In  general,  it  should  not  be  taken  to  indicate  that 
such  seed  will  remain  free  from  the  disease. 

The  fungus  attacks  pods,  stems,  and  leaves,  but  the  most  con- 
spicuous injuries  are  the  spots  upon  the  pods  (Fig.  154).  These 
appear  first  as  small,  brownish, 
or  purplish  discolorations,  and 
as  the  fungus  spreads  radially 
the  central  portion,  becomes 
dark  and  sunken.  Neighbor- 
ing spots  may  also  coalesce,  so 
that  irregular  sunken  patches 
may  result.  The  conidia  in 
quantity  have  a  pinkish  tint, 
and  the  ulcerated  areas  develop 
the  spores  so  profusely  that 
this  color  becomes  pronounced 
under  favorable  conditions. 
The  fungus  may  appear  upon 
the  cotyledons  or  young  hypo- 
cotyls  of  the  seedlings,  and 
this  is  usually  indicative  of 
badly  affected  seed. 

The  fungus.  The  mycelium 
penetrates  the  affected  parts 
to  a  considerable  extent.  The 
bean  seeds  beneath  the  lesions 
on  the  pods  are  commonly 
spotted  or  slightly  discolored, 
and  a  careful  examination 
would  show  that  the  fungous 
hyphae  are  also  present  in 
those  parts.  Distribution  of  the 
fungus  another  year  is  insured 


FIG.  154.   ANTHRACNOSE  OF  BEANS 
(Photograph  by  H.  H.  Whetzel) 


through  such  infected  seed. 

Beneath  the  cuticle  or  epidermis  of  the  older  spots  a  stromatic 
mass  of  hyaline  hyphae  is  developed,  and  from  this  arise  numer- 
ous short  conidiophores  bearing  the  irregularly  elliptical  conidia 
(Fig.  156).  Near  the  margins  of  these  spore  pustules,  or  acervuli, 


324 


FUNGOUS  DISEASES  OF  PLANTS 


FlG.   155.     COLLETOTRICHUM     FROM     BEAN: 

AN  ISOLATION    CULTURE.    (Photograph  by 
Geo.  F.  Atkinson) 


a  few  dark  colored  setae  are  developed.1    The  conidia  measure 
1 5-19  X  3.5-5.5^.    They  germinate  readily  and  usually  become 

septate  during  the  process. 
Each  conidium  is  inclosed 
by  a  gelatinous  envelope 
which  when  dry  glues  it 
to  other  spores  or  to  any 
object  upon  which  it  falls  ; 
when  moist,  however,  the 
spores  are  readily  sepa- 
rated and  distributed. 

Control.  Very  diverse 
methods  of  controlling  this 
important  disease  have 
been  suggested.  Seed  se- 
lection is  important,  but  it 
is  not  sufficient  to  select 
seed  which  do  not  appear 
to  be  infected,  for  many 
minute  infections  will  be  overlooked.  It  is  desirable,  therefore, 
to  select  healthy  seed  from  healthy  pods,  preferably  from  a  field 
which  shows  the  disease  slightly  or  not  at  all.  Whetzel's  experi- 
ments thus  far  seem  to 
indicate  that  this  latter 
type  of  selection  yields 
most  satisfactory  results. 
Spraying  with  Bor- 
deaux mixture,  5-5-50 
formula,  is  to  be  advised 
when  the  disease  ap- 
pears early  and  when  the  facilities  are  at  hand  to  make  a  thorough 
application  of  the  spray.  Burning  infected  material  is  necessary ; 
moreover,  rotation  of  crops  is  important. 

1  The  setae  in  this  case  are  not  commonly  a  conspicuous  part  of  the  acervulus, 
and  in  a  cursory  examination  of  the  fungus  they  may  be  sometimes  overlooked. 
In  fact,  this  fungus  was  at  first  placed  in  the  genus  Glceosporium.  It  is  possible 
that  climatic  conditions  or  the  texture  of  the  host  may  be  important  in  determin- 
ing the  relative  number  of  setae. 


FIG.  156.    COLLETOTRICHUM  LINDEMUTHIANUM 


FUNGI  IMPERFECTI 


325 


XXVII.    ANTHRACNOSE  OF  COTTON 
Colletotrichum  Gossypii  Southworth 

ATKINSON,   G.   F.    Anthracnose  of  Cotton.    Journ.   Mycology  6:   173-178. 

pis.  17-18.    1891. 
ATKINSON,  G.  F.    Some  Diseases  of  Cotton.    Ala.  Agl.'Exp.  Sta.  Built.  41: 

40-49.  figs.  9-13.    1892. 
SOUTHWORTH,  E.  A.   Anthracnose  of  Cotton.   Journ.  Mycology  6:   100-105. 

pi.  4.  figs.  1-8.    1890. 

Habitat  relations.  Anthracnose  of  cotton  exists  as  a  malady  of 
some  importance  upon  rich  land  in  some  of  the  cotton-growing, 
particularly  the 
Gulf,  states.  It 
would  seem  that 
the  fungus  is  widely 
distributed,  but 
serious  injury  is 
doubtless  depend- 
ent upon  local  con- 
ditions. 

The  lesions  of 
this  fungus  are 
more  important 
when  bolls  and 
seedlings  are  in- 
fested, but  injuries 
to  stems  and  leaves 
are  not  uncommon. 
Upon  the  bolls  the 
minute  reddish 
spot  at  first  evi- 
dent about  an  infec- 
tion center  rapidly 
increases  in  size, 

the    injured     area,       FlG.  I5?.   ANTHRACNOSE  OF  COTTON.   (After  Geo.  F. 
marked  by  a  red-  Atkinson) 

dish  border,  becom- 
ing black  and  slightly  depressed.    Many  spots  may  become  conflu- 
ent, so  that  very  irregular  outlines  may  result.   As  the  development 


326  FUNGOUS  DISEASES  OF  PLANTS 

of  conidia  proceeds,  in  the  older  areas  the  spots  vary  from  gray  to 
bright  pink.  Through  such  injuries  the  boll  is  usually  seriously 
damaged  and  may  never  open.  Moreover,  through  the  boll  injuries 
the  fungus  may  probably  penetrate  the  seed  and  thus  be  carried  over 
and  distributed  the  following  season.  Seedlings  may  be  affected 
either  upon  cotyledons  or  stem,  especially  upon  employing  diseased 
seed,  and  at  this  stage  the  plantlet  is  readily  wilted  as  a  result. 

Upon  stems  of  the  adult  plant  the  Colletotrichum  seems  to  be 
largely  a  wound  parasite,  although  in  continued  moist  weather 
direct  injury  may  be  induced.  Upon  mature  leaves  it  is  said  to 
take  the  form  of  a  scald,  or  frost  effect,  and  it  may  also  accompany 
other  leaf  diseases. 

Characters  of  the  fungus.  From  a  loose  stroma  within  the  tis- 
sues conidiophores  of  two  types  break  through  the  epidermis  and 
produce  conidia  abundantly.  Small  hyaline  conidiophores,  usually 
less  than  twice  the  length  of  the  conidia,  are  more  numerous,  and 
they  arise  in  a  compact  mass,  each  abscising  one  conidium  after 
another.  The  spores  are  (see  Southworth)  4.5-7  X  1 5-20/4,  oblong, 
the  diameter  of  the  middle  portion  sometimes  less  than  at  the  ends, 
usually  pointed  at  the  base,  and  vacuoles  may  be  present.  The 
other  form  of  the  conidiophores,  termed  setae,  arise  later  from  dark 
colored  cells  of  the  stroma.  These  setae,  which  usually  appear  in 
clusters  of  5  to  10,  are  of  a  dark  olive  color,  100  to  250/4  long, 
tapering  and  septate.  They  bear  ovate,  basally  pointed  spores. 
The  mass  of  conidiophores  and  spores  produced  in  this  manner 
constitute  the  acervuli.  In  this  form  an  acervulus  may  be  from 
100  to  150/4  in  diameter. 

The  spores  germinate  readily  in  almost  any  nutrient  media,  usu- 
ally becoming  once  or  twice  septate  during  germination.  The  my- 
celium, which  grows  vigorously  in  culture,  is  hyaline,  flexuous, 
and  abundantly  septate.  Short  conidiophores  are  promptly  pro- 
duced. The  conidia  are  borne  singly,  but  by  virtue  of  a  slightly 
gelatinous  envelope  they  may  adhere  in  a  crown  about  the  tip 
of  the  conidiophore.  Appressoria  are  also  produced  by  the  myce- 
lium, and  these  give  rise  to  other  similar  structures,  to  an  ordinary 
hypha,  or  to  a  conidiophore.  Such  dark  cells  are  also  developed 
from  a  germ  tube  when  germination  proceeds  in  water.  The  setae 
have  also  been  produced  in  culture. 


FUNGI   IMPERFECTI  327 

Control.  Adequate  methods  of  control  have  not  been  devel- 
oped. It  is  important,  however,  to  select  varieties  which  permit 
the  access  of  light  to  the  bolls.  Seed  selection  from  healthy  bolls 
may  prove  of  value. 

XXVIII.    WITHER-TIP  AND  SPOT  OF  CITRUS  FRUITS 
Colletotrichum  Glceosporioides  Penz. 

ROLFS,  P.  H.    Wither-Tip  and  Other  Diseases  of  Citrus  Trees  and  Fruits. 
Bureau  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  52:   1-20.    pis.  1-6.    1904. 

Host  relations.  In  practically  all  parts  of  the  world  in  which  the 
orange  and  other  citrus  fruits  are  cultivated  this  fungus  is  more 
or  less  common.  The  diseases  or  injuries  produced  by  it  are  vari- 
ously known  as  wither-tip,  leaf  spot,  anthracnose,  canker,  and  lemon 
spot,  depending  upon  the  effects  upon  the  host.  The  fungus  is  a 
far  more  active  parasite  in  humid  regions,  and  in  Florida,  particu- 
larly, the  disease  appears  to  be  growing  in  importance  from  year 
to  year.  In  1891  it  was  casually  noted  by  Underwood,  and  since 
that  time  it  has  rapidly  come  into  prominence  as  a  destructive 
agent  to  the  citrus  industries. 

On  orange.  The  wither-tip  effect  is  particularly  characteristic  of 
orange  trees.  It  may  be  found  upon  trees  of  all  ages,  affecting  and 
killing  back  the  tips  of  the  branches.  On  large  trees  this  neces- 
sarily prevents  the  setting  of  a  heavy  crop  of  fruit.  The  varieties 
of  the  orange  seem  to  be  about  equally  affected.  The  disease  is 
easily  distinguished  from  dieback  (a  disease  not  associated  with 
a  specific  organism)  by  unmistakable  characters,  especially  by  the 
ashen  color  of  the  twigs  where  dieback  effects  are  brown  ;  by 
the  line  or  ring  separating  injured  from  healthy  tissue,  which  is 
absent  in  the  other  disease ;  by  the  absence  of  any  resinous  de- 
posit ;  and  by  the  frost-like  killing  of  twigs,  where  in  dieback 
twisted  branches  and  the  development  of  twigs  with  brown-stained 
bark  are  common. 

On  lemon.  Upon  the  lemon  it  causes  not  only  a  wither-tip,  but 
also  a  very  definite  leaf  spot,  and  from  the  diseased  areas  of  the 
leaf  the  fungus  may  extend  into  the  twigs,  thus  resulting  in  the 
wither-tip,  the  more  acute  form  of  the  trouble.  The  mature  fruit 
may  also  be  affected  in  the  form  of  a  fruit  spot.  It  would  appear 


328  FUNGOUS  DISEASES  OF  PLANTS 

that  penetration  of  the  fruit  is  probably  gained  through  some  in- 
jury or  abrasion.  A  dark  spot  is  invariably  produced,  but  ordina- 
rily no  rot  results.  The  spot  on  the  fruit,  however,  may  not  manifest 
itself  before  shipment  to  market,  and  therefore  the  quality  of  a 
large  shipment  may  be  materially  affected. 

On  the  lime.  Upon  the  lime  practically  all  forms  of  the  disease 
are  to  be  seen,  and  it  is  the  host  which  is  most  seriously  affected. 
It  occurs  as  wither-tip,  and  the  infection  is  through  the  terminal 
bud.  It  may  also  occur  as  a  fruit  canker,  and  more  particularly  as 
an  "  anthracnose  "  on  the  young  growing  shoots. 

The  fungus.  According  to  Rolfs,  the  acervuli  are  produced  in 
many  of  the  diseased  areas,  whether  of  leaf,  twig,  or  fruit.  The 
spores  are  produced  on  short  conidiophores,  among  which  are  inter- 
spersed, especially  at  the  margin  of  the  acervuli,  certain  fuliginous 
setae,  from  60  to  160/4  long,  and  once  or  twice  septate.  There 
are,  however,  smaller  setae  throughout;  yet  on  tender  twigs  few 
setae  may  appear.  The  conidia  develop  from  short  conidiophores 
3  to  1 8/*,  arising  from  a  more  or  less  definite  stroma. 

Control.  It  has  been  found  that  the  disease  may  be  held  in 
check  by  proper  spraying,  especially  with  Bordeaux  mixture.  The 
time  of  spraying,  however,  depends  upon  the  form  of  the  disease, 
wither-tip  and  leaf  spot  being  preferably  pruned  out  and  the  trees 
subsequently  sprayed.  The  fruit  of  the  lemon  will  not,  however, 
permit  of  the  use  of  Bordeaux,  and  the  lemon  spot  may,  there- 
fore, be  best  controlled  by  sprinkling  the  fruit  with  ammoniacal 
solution  of  copper  carbonate  before  picking. 

XXIX.   ANTHRACNOSE  OF  CLOVER  AND  ALFALFA 
Colletotrichum  Trifolii  Bain 

BAIN,  S.  M..  and  ESSARY,  S.  H.    Selection  for  Disease-Resistant  Clover. 

Tenn.  Agl.  Exp.  Sta.  Built.  75  (Vol.  19,  No.  i):    i-io.  figs.  1-5.    1906. 
BAIN,  S.  M.,   and  ESSARY,  S.  H.    A  New  Anthracnose  of  Alfalfa  and  Red 

Clover.    Journ.  Mycology  12 :    192,193.    1908. 

An  investigation  of  the  causes  of  failure  in  red  clover  growing 
in  Tennessee  has  resulted  in  the  discovery  of  an  anthracnose  as  the 
chief  agent.  This  fungus  attacks  also  alfalfa,  but  alsike  clover  is 
practically  immune.  The  fungus  has  been  reported  also  from 
West  Virginia  and  Arkansas. 


FUNGI   IMPERFECTI  329 

The  fungus  produces  black  spots  on  stems  and  petioles,  very 
rarely  on  the  leaves.  It  is  stated  that  the  plants  seem  to  suffer  the 
greatest  injury,  first,  when  the  seedlings  encounter  prolonged  dry 
weather ;  and  again,  during  the  ripening  of  the  seed,  —  when  the 
effects  are  more  severe  on  the  stems  just  above  the  surface  of  the 
ground.  The  conidia  are  hyaline,  generally  straight  and  rounded, 
11-13  x  3-4/4.  The  setae  are  continuous  or  I -septate,  fuliginous, 
apex  pale,  39-62  x  4-7  /4,  often  sinuous  or  nodulose.  It  is  improba- 
ble that  any  cultural  methods  would  be  effective  in  preventing  the 
spread  of  this  disease.  Selection  of  seed  from  apparently  resistant 
plants  have  yielded  offspring  which  likewise  developed  the  disease 
to  less  extent.  It  remains,  however,  to  be  seen  if  this  may  not  be 
due  in  part  to  clean  seed  selection. 

XXX.  ANTHRACNOSE  OF  SNAPDRAGON 

Colletotrichum  Antirrhini  Stewart 

STEWART,  F.  C.    An  Anthracnose  and  a  Stem  Rot  of  the  Cultivated  Snap- 
dragon.   N.  Y.  Agl.  Exp.  Sta.  179:  105-109.    1900. 

The  above  fungus  is,  according  to  Stewart,  the  most  serious 
disease  of  the  snapdragon  (Antirrhinum  majus],  as  cultivated  in 
greenhouses  in  the  United  States.  It  is  also  destructive  in  the 
garden.  In  greenhouses  the  greatest  injury  occurs  generally  in  the 
spring  and  fall,  and  in  the  open  during  late  summer.  It  attacks 
both  stems  and  leaves  at  practically  any  stage  of  growth. 

On  the  leaves  circular  dead  spots  are  produced,  and  on  the 
stems  elliptical  sunken  areas  3-10  mm.  in  length.  The  spots  on 
the  stems  frequently  become  confluent,  and  girdling  may  some- 
times result. 

Small  dark  stromata  are  produced  in  the  centers  of  these  spots, 
each  under  favorable  conditions  becoming  an  acervulus  by  produc- 
ing short  conidiophores  bearing  straight  or  slightly  curved  conidia, 
1 6-2 1  x  4/4,  and  also  several  dark,  tapering  setae,  50-100/4  long. 

Cuttings  should  be  made  from  healthy  plants  only,  and  over- 
head watering  avoided  when  possible.  If  it  is  necessary  to  spray 
young  plants,  Bordeaux  mixture  is  effective  ;  but  a  fungicide  which 
does  not  discolor  the  foliage  should  be  substituted  if  further  treat- 
ments are  required. 


330  FUNGOUS  DISEASES  OF  PLANTS 

XXXI.    COLLETOTRICHUM:  OTHER   SPECIES 

Among  numerous  other  species  of  economic  importance  the 
following  may  be  mentioned. 

Colletotrichum  Lagenarium  (Pass.)  Ell.  &  Hals.  The  anthrac- 
nose  of  cucumbers,  squash,  watermelons,  etc.,  is  a  disease  of  both 
leaves  and  fruit.  On  the  former  brown  spots  are  produced,  causing 
early  maturity  of  the  leaf ;  but  the  more  serious  form  of  the 
trouble  is  on  the  fruit,  where  water-soaked,  finally  sunken  spots 
are  developed.  In  these  spots  appear  acervuli  producing  numerous 
conidia  adhering  in  the  form  of  viscid  masses  pink  in  color.  A 
mold-like  growth  of  superficial  hyphae  may  also  appear  in  moist 
weather.  In  time  the  whole  fruit  may  rot,  saprophytic  organisms 
assisting. 

Colletotrichum  falcatum  Sacc.  is  believed  to  be  the  chief  cause 
of  the  red  rot1  of  sugar  cane  (Sacckarum  officinaruni)  in  the 
East  Indies  and  in  the  Hawaiian  Islands. 

Colletotrichum  Phomoides  (Sacc.)  Chester2  is  the  cause  of  a 
disease  of  the  tomato  fruit  characterized  by  discolored,  sunken 
spots.  Under  moist  conditions  these  spread  quickly,  become  con- 
fluent, and  there  is  produced  a  general  decay.  At  first  distinct 
acervuli  are  produced,  but  with  the  softening  of  the  tissues  a  con- 
tinuous stratum  of  conidiophores  and  setae  may  arise.  This  is  re- 
garded as  wholly  distinct  from  a  species  on  peppers,  Colletotrichum 
nigrum  Ell.  &  Halsted,  described  a  few  years  earlier. 

XXXII.    GLCEOSPORIUM 

The  genus  Glceosporium  has  been  discussed  in  part,  inas- 
much as  several  species  of  this  form  genus  have  been  definitely 
connected  with  several  genera  of  Ascomycetes  already  treated. 
Specific  names  have  been  assigned  to  forms  of  this  genus  on 
several  hundred  host  plants.  Many  of  these  are  fungi  of  great 
economic  importance.  They  are  parasites  whose  attacks  frequently 
amount  to  epidemics.  Nevertheless,  these  fungi  are  grown  in 
artificial  cultures,  as  a  rule,  with  the  greatest  readiness.  Moreover, 

1  Lewton-Brain,  L.    Red    Rot   of    the   Sugar  Cane   Stem.    Exp.    Sta.   of   the 
Hawaiian  Sugar  Planters  Assoc.  Built.  8  :   1-44.  figs.  1-13.    1908. 

2  Chester,  F.  D.    Diseases  of  the  Tomato  and  Their  Treatment.    Del.  Agl.  Exp. 
Sta.  Rep.  4:  60-62.  figs.  S-io.    1891. 


FUNGI  IMPERFECTI 


331 


such  cross-inoculation  experiments  as  have  been  made  indicate 
that  many  species,  at  least,  are  not  closely  restricted  as  to  hosts, 
and  one  form  might  be  the  cause  of  disease  in  a  variety  of  plants. 
It  has  seemed  to  be  a  group  which  would  well  reward  comparative 
study  in  artificial  culture,  and  advantage  has  been  taken  of  this 
by  Stoneman,1  Edgerton,1  and  others.  With  particular  reference 
to  species  of  one  type,  those  which  may  represent  stages  of  the 
pyrenomycetous  genus  Glomerella,  Edgerton  says  in  part : 

There  are  many  closely  related  forms  and  species  and  all  are  variable. 
They  vary  under  artificial  cultivation  and  probably  under  natural  conditions. 
Many  are  similar  enough  to  be  considered  the  same  species,  but  evidence  suffi- 
cient to  warrant  bringing  together  the  related  forms  as  one  species  is  generally 
lacking. 

In  the  determination  of  a  species  too  much  dependence  cannot  be  placed 
upon  cultural  characters  alone.  These  characters  are  useful,  but  are  not  suffi- 
ciently constant  to  justify  exclusive  use. 

Thus  far  species  of  Glceosporium  seem  to  have  been  definitely 
connected  with  three  genera  of  Ascomycetes,  as  follows  :  Pseudope- 
ziza,  Glomerella,  and  Gno- 
monia,  the  imperfect  stages 
of  which  were  respectively 
known  as  Glceosporium 
Ribis  (Lib.)  Mont.  & 
Desm.,  Glceosporium  fruc- 
tigenum  Berk.,  and  Glceo- 
sporium nerviseqtium  Sacc. 
The  imperfect  form  is  in- 
variably the  important 
stage  from  the  phytopatho- 
logical  point  of  view.  The 
effects  upon  the  hosts  are 


FIG.  158.   GLCEOSPORIUM  ON  LEAVES  OF 
NORWAY  MAPLE 


in  every  way  comparable 
to  those  resulting  from  the 
attacks  of  various  species 

placed  in  the  closely  related  genus  Colletotrichum  previously  de- 
scribed. In  fact,  some  species  of  Glceosporium  occasionally  pro- 
duce a  small  number  of  setae  under  special  conditions.  Upon  the 


1  See  Bitter  Rot  of  the  Apple,  p.  271. 


332  FUNGOUS  DISEASES  OF  PLANTS 

twig  cankers  the  glceosporial  stage  of  the  apple  bitter  rot  fungus 
may  produce  these.  Moreover,  in  artificial  cultures  species  of  Colle- 
totrichum  have  also  yielded  ascigerous  stages  referable  to  the  genus 
Glomerella.1  On  the  other  hand  there  is  a  fairly  close  relationship 
between  extreme  forms  of  Colletotrichum  and  Volutella. 

In  members  of  both  Colletotrichum  and  Glceosporium  it  has  long 
been  known  that  when  conidia  germinate  in  a  drop  of  water  on  a 
glass  slide,  or  under  certain  other  conditions,  structures  resembling 
secondary  or  resting  spores  may  be  formed.  Hasselbring2  has 
made  a  special  study  of  these  and  concludes : 

The  spore-like  organs  formed  by  the  germ  tubes  of  the  anthracnoses  are 
adhesion  organs,  by  means  of  which  the  fungus  is  attached  to  the  surface  of 
its  host  during  the  early  stages  of  infection.  They  are  not  suited  for  dissemi- 
nation and  therefore  are  not  to  be  regarded  as  spores.  The  adhesion  discs  are 
formed  as  a  result  of  stimuli  from  mechanical  contact  acting  on  the  germ  tubes. 
When  growing  in  nutrient  media  the  germ  tubes  lose  their  power  of  reacting 
to  contact  stimuli  by  the  formation  of  appressoria.  Under  natural  conditions 
the  appressoria  are  formed  as  soon  as  the  germ  tube  emerges  from  the  spore. 

XXXIII.    ANTHRACNOSE  OF  GRAPE 
Glceosporium  ampelophagum  Sacc. 

SCRIBNER,  F.  L.  Report  on  Fungous  Diseases  of  the  Grape  Vine.  Anthrac- 
nose.  Division  of  Botany,  U.  S.  Department  of  Agriculture,  Built.  11 : 
34-38.  pi.  6.  1886. 

VIALA,  T.  Les  Maladies  de  la  Vigne.  Anthracnose.  pp.  204-247.  pis.  5-6. 
Jigs.  60-73.  I893- 

The  anthracnose  or  bird's-eye  disease  of  the  grape  is  a  striking 
disease  now  well  distributed  throughout  Europe  and  America.  It 
was  not  observed  extensively  in  the  United  States  until  about  1885, 
and  there  are  few  localities  in  which  it  has  become  a  malady  so 
constant  in  succeeding  seasons  as  the  black  rot  or  the  downy 
mildew.  It  is,  however,  a  disease  which  may  cause  great  injury 
when  it  becomes  epidemic,  particularly  in  view  of  the  fact  that  it 
is  not  so  readily  treated. 

The  disease  occurs  upon  berries,  shoots,  and  leaves,  but  is  far  more 
common  upon  shoots  and  berries.  Upon  the  latter  the  well-known 

1  Edgerton.    Bot.  Gaz.  46,  /.  c. 

2  Hasselbring,  H.  H.    The  Appressoria  of  the  Anthracnoses.    Bot.  Gaz.  42  : 
135-142.  figs.  1-7.    1906. 


FUNGI  IMPERFECTI  333 

bird's-eye  spots,  or  effects,  are  produced.  At  first  ashen-brown 
spots  appear,  and  as  these  enlarge  in  a  more  or  less  regular  man- 
ner the  central  portion  becomes  sunken,  and  between  the  paler 
central  portion  and  the  brown  outer  border  a  band  of  red  or  red- 
purple  is  apparent.  The  unaffected  portion  of  the  berry  remains 
perfectly  green,  but  the  spot  may  at  times  embrace  eventually  the 
entire  berry.  When  the  shoots  are  affected  the  spots  are  similar 
to  those  on  the  fruit  except  that  they  elongate  in  the  direction 
of  the  axis,  becoming  prominently  sunken,  pale  at  the  center,  and 


FIG.  159.    GLCEOSPORIUM  AMPELOPHAGUM:  ANTHRACNOSE  OF  GRAPE 

always  less  highly  colored.    The  young  leaves  are  also  affected  with 
spots  with  pale  centers  and  brown-red  borders. 

The  acervuli  of  the  fungus  appear  more  commonly  upon  berries 
and  twigs.  The  fungus  resembles  very  closely,  in  general,  other 
species  of  Gloeosporium.  A  large  number  of  minute  conidiophores 
are  produced,  each  of  which  may  originate  many  conidia.  The  latter 
may  be  elliptical,  ovate,  oblong,  or  even  slightly  constricted  at  the 
middle  portion.  These  are  usually  5-6  x  2. 5-3. 5  ft.  By  some  it 
has  been  claimed  that  the  anthracnose  of  the  grape  is  the  same 
fungus  as  that  producing  the  bitter  rot  of  the  apple,  but  this  is 
probably  incorrect.  It  is  quite  probable  that  a  ripe  rot  of  the  grape 


334  FUNGOUS  DISEASES  OF  PLANTS 

may  be  induced  by  Glomerella  rufomaculans ,  the  fungus  of  bitter 
rot ;  but  the  typical  anthracnose  has  not  been  produced  by  inocu- 
lations with  the  apple  fungus.  Moreover,  the  species  here  discussed 
seems  to  be  more  closely  restricted  in  its  conditions  of  growth. 
Upon  artificial  media  it  grows  slowly  and  with  less  vigor  than  is 
commonly  the  case  with  many  species  of  anthracnose. 

Control.  Experiments  concerned  with  the  prevention  of  this  dis- 
ease indicate  that  the  usual  spraying  operations  as  recommended 
for  the  black  rot  are  not  necessarily  effective  for  the  anthracnose. 
Nevertheless,  it  is  doubtful,  under  ordinary  circumstances,  if  other 
precautions  need  be  taken.  When  the  fungus  appears  in  an  epi- 
demic form  it  will  be  necessary  not  only  to  spray  repeatedly  with 
Bordeaux,  but  also  to  prune  out  and  burn  as  promptly  as  possible 
the  diseased  canes  and  fruit  bunches. 


XXXIV.    ANTHRACNOSE   OF  RASPBERRY  AND   BLACKBERRY 

Gloeosporium  Venetum  Speg. 

DETMERS,  FREDA.    Anthracnose  of  Raspberry  and  Blackberry.    Ohio  Agl. 

Exp.  Sta.  Built.  4  (No.  6):  124-126.  pis.  3-4.    1891. 
PADDOCK,  W.    Anthracnose  of  the  Black  Raspberry.    N.  Y.  Agl.  Exp.  Sta. 

Built.  124:  261-274.    1897. 
SCRIBNER,  F.  L.    Anthracnose  of  the  Raspberry  and  Blackberry.    U.  S.  Dept. 

Agl.  Rept.  (1887):  357-367-  pi.  5- 

This  fungus  produces  the  well-known  anthracnose  of  raspberries 
and  blackberries  (Rubus  spp.),  characterized  by  injuries  of  the 
canes.  Raspberries  are  commonly  more  seriously  affected.  Small 
purplish  spots  appear  at  first,  later  the  center  becomes  gray  and 
sunken,  giving  somewhat  the  bird's-eye  effect.  Petioles  and  veins 
of  leaves  may  also  be  affected,  and  the  injuries  are  severe.  Minute 
spots  sometimes  appear  on  the  blade  of  the  leaf.  The  acervuli 
appear  frequently  in  the  older  spots.  Control  measures  have  not 
been  as  effective  as  may  be  possible.  The  pruning  out  and  destruc- 
tion of  diseased  canes  is  essential,  and  thorough  spraying  with 
Bordeaux  may  be  practiced  during  the  early  part  of  the  season. 
Spraying  alone  is  not  ordinarily  sufficient  for  the  proper  control 
of  this  disease.  Healthy  plants  only  should  be  set,  and  a  short 
rotation  practiced. 


FUNGI  IMPERFECTI  335 

XXXV.    GLCEOSPORIUM:    OTHER   SPECIES 

In  addition  to  the  preceding,  and  to  the  various  fungi  already 
discussed  which  have  glceosporial  stages,  the  following  inducing 
diseases  of  some  shrubs  or  trees  may  be  briefly  cited. 

Gloeosporium  Tiliae  Oudem.1  occurs  throughout  a  large  portion 
of  northern  Europe  as  an  important  parasite  of  the  linden  (Tilia 
Ulmifolia).  In  late  spring  the  clear,  circular  spots  appear  upon  the 
leaves,  generally  irregularly  distributed  and  becoming  with  age 
yellowish  brown  and  separated  from  the  healthy  tissue  by  a  darker 
brown  line.  The  spots  may  also  occur  on  the  leafstalks  and  on 
the  twigs  as  small,  sunken  areas.  Severe  attacks  upon  the  leaf- 
stalks cause  a  premature  defoliation.  The  acervuli  appear  most 
abundantly  upon  the  upper  surfaces  of  the  spots.  The  conidia  are 
generally  ovate,  elliptical  or  falcate,  and  measure  10-18  x  4-6/1. 

Gloeosporium  Juglandis  (Lib.)  Mont,  is  a  cause  of  a  serious  leaf 
blight  of  the  butternut  (Juglans  cinered).  The  fungus  has  been 
found  practically  throughout  the  range  of  the  butternut.  The  effects 
of  the  fungus  have  often  been  severe  in  the  northeastern  states, 
where  almost  complete  defoliation  of  some  trees  has  been  noted 
as  early  as  the  latter  part  of  July  in  New  York,  and  early  August 
in  Massachusetts.  Quite  generally  the  fungus  causes  a  defoliation 
which  is  earlier  than  the  normal.  The  leaves  affected  are  covered 
with  irregular  brown  spots,  which  rapidly  induce  ripening,  and 
defoliation  results. 

Gloeosporium  cingulatum  Atkinson2  is  an  anthracnose  of  the 
privet  (Ligustrum  vulgare).  The  fungus  attacks  the  young  twigs, 
producing  at  first  small  dark,  sunken  spots,  but  eventually  girdling 
and  killing  the  twigs.  It  is  considered  distinct  from  Glceosporitim 
Ligustrinum  Sacc. 

Gloeosporium  laeticolor  Berk.,  while  widely  distributed,  occurring 
particularly  upon  peaches  and  apricots,  has  apparently  never  been 
reported  of  serious  importance  in  the  orchard. 

Gloeosporium  apocryptum  E.  &  E.  on  leaves  and  young  twigs 
of  the  Norway  maple  is  an  important  disease  in  the  nursery. 

1  Laubert,  R.    Eine  wichtige  Gloeosporium  Krankheit  der  Linden  Zeitsch.  f. 
Pflanzenkr.    14:  257-262.  pi.  6.    1904. 

2  Atkinson,  Geo.  F.    A  New  Anthracnose  of  the  Privet.    Cornell  Agl.  Exp.  Sta. 
Built.  49  :  306-314.  figs.  1-4.    1892. 


336  FUNGOUS  DISEASES  OF  PLANTS 

XXXVI.    MARSONIA 

Marsonia  Populi  (Lib.)  Sacc.1  is  a  common  leaf  spot  or  anthrac- 
nose  of  many  species  of  poplar  (Populus)  in  Europe  and  America. 
It  is  more  frequently  seen  upon  the  white  poplar  (Populus  alba). 
It  is  often  a  destructive  fungus  in  the  nursery.  It  may  also  appear 
as  a  twig  blight.  The  young  leaves  may  be  killed  and  the  fungus 
may  even  extend  to  the  main  shoot  and  branches,  or  it  may  occur 
upon  the  twigs  in  isolated  black  spots.  When  somewhat  older, 
nursery  stock  may  show  black  spots  at  the  older  nodes,  indicating, 
apparently,  infection  through  the  leaves. 

Marsonia  ochroleuca  B.  &  C.,  causing  a  leaf  spot  of  chestnut,  is 
a  fungus  which,  while  far  less  dangerous  to  the  general  growth  of 
the  chestnut  tree  -than  the  canker,  is  far  more  widely  distributed, 
and  seems  to  occur  wherever  the  chestnut  is  known.  It  is  frequently 
injurious  to  a  noticeable  extent.  Klebahn 2  has  demonstrated  a 
connection  between  one  species  of  Marsonia,  Marsonia  Juglandis, 
and  Gnomonia  leptostyla. 

XXXVII.    PEACH  BLIGHT 
Coryneum  Beijerinckii  Oudem. 

SMITH,  R.  E.    California  Peach  Blight.    Cal.  Agl.  Exp.  Sta.  Built.  191 :  73- 
100.  figs.  1-16.    1906. 

Habitat  relations.  It  is  somewhat  difficult  to  determine  the 
extent  of  injury  caused  by  this  fungus,  since  references  to  a  disease 
produced  by  this  or  related  fungi  have  not  always  been  clearly  dif- 
ferentiated from  other  peach  diseases.  In  recent  years,  however, 
this  disease  has  been  studied  in  California,  where  it  has  been  un- 
usually prevalent,  causing  great  destruction  during  1905-1906. 
The  organism  had  become  gradually  very  abundant,  and  the  sea- 
sons were  favorable  to  its  continued  spread.  In  general,  the  effect 
of  the  fungus  is  to  kill  the  buds  on  the  fruiting  wood,  to  produce 
spots  on  the  green  twigs,  to  retard  the  development  of  the  leaves, 
and  to  cause  dropping  of  the  fruit.  Accompanying  the  activity  of 
this  fungus  is  a  notable  gumming  of  the  twigs  from  the  dead  spots, 
this  being  particularly  abundant  during  moist  conditions.  It  will 

1  Halsted,  B.  D.    Poplar  Blight  in  the  Nursery.    N.  J.  Agl.  Exp.  Sta.  Kept.  15  : 
349-396.    1894. 

2  Klebahn,  H.    Centrbl.  f.  Bakt.  u.  Infekskr.  15  (2  Abt.) :  336.    1905. 


FUNGI  IMPERFECTI 


337 


be  seen,  therefore,  that  many  symptoms  of  the  disease  as  described 
in  California  are  more  or  less  identical  with  Clasterosporium  car- 
pophilum  (Lev.)  Aderh.,  as  described  by  McAlpine1  in  Australia. 
It  also  occurs  in  Algeria.2  According  to  Smith,  the  fungus  could 
not  be  mistaken  for  a  simple  hyphomycete,  as  shown  by  the  ag- 
gregate conidiophore  production  (Fig.  160).  The  conidial  stage 
of  the  fungus  is  produced  both  on  leaves  and  shoots,  the  pustules 
appearing  at  the  center  of  the  spots.  They  are,  however,  not 
readily  observed,  since  the  spots  on  young  shoots  are  often  sterile 
and  those  upon  the  leaves  may 
fall  out  before  the  production  of 
spores.  Perhaps  the  most  unfortu- 
nate phase  of  this  disease  is  kill- 
ing of  winter  buds,  which  of  course 
greatly  destroys  the  vitality  with 
respect  to  fruit  production  the  fol- 
lowing season.  It  is  quite  probable 
that  this  fungus  is  the  same  as 
Helminthosporium  carpophilum 
(Lev.),  and  this  is  also  the  view 
of  McAlpine. 

Control.  In  controlling  this  dis- 
ease, it  has  become  evident  that 
winter  spraying  is  essential.  The 
disease  is  reported  to  make  its 
appearance  early  in  January  in  Cal- 
ifornia, and  generally  somewhat  prior  to  the  activity  of  the  winter 
buds.  The  spraying  which  may  be  given  for  prevention  of  leaf 
curl  is  ordinarily  too  late  for  the  best  results  upon  this  blight  fungus. 
It  is  recommended,  therefore,  that  an  additional  spraying  in  Cali- 
fornia be  given  in  November  or  December  to  assist  in  controlling 
this  blight  organism.  If  a  single  spraying  only  can  be  given,  it  is 
perhaps  best  to  give  it  in  December,  but  later  than  early  January 
under  California  conditions  is  ineffective. 


FlG.   1 6O.      CORYNEUM   BEiyERINCKII 

(After  R.  E.  Smith) 


1  McAlpine,  D.  Fungous  Diseases  of  the  Stone  Fruits  in  Australia,,  and  Their 
Treatment.    1902. 

2  Trabut,   L.   Le   Coryneum.    Maladies  des  arbres   a  noyaux.    Built,   agr.  de 
1'Algerie  et  de  la  Tunisie  10  :   1904. 


338 


FUNGOUS  DISEASES  OF  PLANTS 


XXXVIII.    LEAF  BLIGHT   OF  CRANBERRY 

Pestalozzia  Guepini  Desm.  var.  Vacdnii  Shear 

SHEAR,  C.  L.    Cranberry  Diseases.    Bureau  Plant  Ind.  U.  S.  Dept.  Agl.  Built. 
110:  38-39-    I9°7- 

This  fungus  is  often  found  upon  the  cranberry,  but  it  is  doubt- 
less of  minor  importance  as  affecting  the  production  of  berries.  It 
occurs  upon  fruit  and  leaves.  The  appear- 
ance of  affected  berries  is  not  particularly 
characteristic.  The  conidia  are  produced 
in  quantity  upon  affected  leaves  placed  in  a 
moist  chamber.  The  conidia  are  usually 
four-septate  with  the  three  central  cells 
dark  colored.  The  hyaline  apical  cell  is 
furnished  with  from  three  to  four  filiform 


FIG.  161.    PESTALOZZIA  GUEPINI.    (After  Shear) 
a,  acervulus  ;  £,  conidia ;  c  and  d,  germinating  conidia 

appendages,  and  the  basal  cell  has  a  single  shorter  appendage. 
It  is  interesting  to  note  that  in  the  germination  of  this  fungus 
one  or  more  germ  tubes  are  developed  from  the  basal  hyaline  cell. 
The  fungus  grows  vigorously  in  artificial  culture.  The  mycelium 
is  hyaline,  and  it  develops  a  pinkish  color-  when  the  acervuli  are 
formed.  The  spores  appear  in  about  ten  days  after  sowings  are 
made  if  conditions  are  favorable. 

Pestalozzia  Hartigii  Tub.  is  a  fungus  of  importance  in  forest 
tree  nurseries  where  it  attacks  the  seedlings  of  young  trees  of  pine 


FUNGI   IMPERFECTI 


339 


and  other  conifers,  as  well  as  those  of  some  deciduous  trees,  caus- 
ing a  shrinking  of  the  bark  around  the  young  stem,  and  later  a 
swelling  above  the  injured  area.  The  affected  portions  may  be 
killed,  and  the  injury  results  in  time  in  the  death  of  the  plant. 


XXXIX.    SHOT-HOLE  DISEASE  OF  PLUM  AND  CHERRY 
Cylindrosporium  Padi  Karst 

ARTHUR,  J.   C.    Plurh-Leaf   Fungus.    N.  Y.  Agl.  Exp.   Sta.   Rept.  8 :   293- 

298.  figs.  6-10.    1889. 
STEWART,  F.  C.,  and  EUSTACE,  H.  J.    Shot-Hole  Fungus  on  Cherry  Fruit 

Pedicels.    N.  Y.  Agl.  Exp.  Sta.  Rept.  20:  146-148. 

Host  relations.    Many  of  the    leaf -spot  fungi  occurring   upon 
certain  varieties  of  plums,  cherries,  and  other  stone  fruits  are  to  a 

considerable  extent  "  shot-    , . "' 

hole  "fungi.  In  such  cases 
the  more  or  less  circular 
injured  area  is  separated 
by  a  line  of  cleavage  from 
the  healthy  tissue,  the  in- 
jured tissue  within  this 
area  promptly  contracting, 
drying,  and  falling  out. 
Cylindrosporium  is  respon- 
sible for  the  greater  portion 
of  this  shot-hole  trouble  on 
many  varieties  of  plums 
and  cherries  in  America. 
On  some  varieties  of  the 
domestica  type,  as  also  on 
some  cherries,  the  fungus 
may  be  common,  produc- 
ing spots  only,  or  with 
inconspicuous  shot-hole 
effects.  This  is  also  true 
of  the  Mahaleb  cherry. 
The  Japanese  plums,  on 
the  other  hand,  show  a 


FIG.  162.   SHOT-HOLE  DISEASE  OF  CHOKE 
CHERRY 


340 


FUNGOUS  DISEASES  OF  PLANTS 


very  pronounced  shot-hole  effect.    Varieties  of  Prumis  americana 
are  frequently  free  from  this  fungus. 

Where  a  species  or  variety  is  subject  to  shot-hole  diseases  a  shot- 
hole  effect  may  also  be  produced  upon  the  leaves  by  spraying  with 
any  substance  injurious  to  the  leaf.  When  the 
leaves  are  so  severely  injured  that  the  spots  coa- 
lesce, the  large  irregular  pieces  may  fall  out  in 
the  same  manner  as  just  indicated.  In  any 
case  the  effects  of  shot-hole  troubles  on  the  leaf 
are  frequently  very  severe,  so  that  practically 
complete  defoliation  of  the  trees  may  take  place 
by  midsummer. 

The  fungus.    In  many  cases  the  development 
of  the  acervuli  of  the  fungus  is  not  evident  before 
the  diseased  areas  have  fallen  away,  but  varieties 
in  which  the  injured  areas  are  persistent  exhibit 
the  fruiting  pustules  in  great  quantity.    In  such 
cases  the  spores  may  be  seen  to  issue  from  the 
acervulus  in  tendril-like  masses  which  are  quickly 
spread  out  over  the  surface  by  dew  and  other 
agencies,  appearing  at  first  as  a  pale  or  ashen 
coating,  becoming  darker  after  a  few  days.     The  conidiophoric 
layer  is  often  extensive  and  closely  beset  with  the  minute  conidio- 
phores  (Fig.  164).    The  spores  are  curved  and  measure  ordinarily 


FIG.  163.  CULTURE 

OF   CYLINDROSPO- 

RIUM  PADI 


FIG.  164.    CYLINDROSPORIUM  PADI 
a,  section  of  acervulus  ;  £,  conidia,  some  germinating 


FUNGI  IMPERFECT!  341 

48-60  x  2  p.  They  germinate  readily,  and  evidently  require  but  a 
few  days'  incubation  after  infection  for  the  production  of  the  char- 
acteristic shot-holes  upon  susceptible  hosts. 

No  ascogenous  stage  of  this  fungus  is  known,  and  there  is  some 
doubt  as  to  the  ordinary  method  of  wintering  over.  Stewart,  how- 
ever, has  found  the  pustules  of  this  fungus  on  the  twigs  of  cherry, 
and  it  is  quite  probable  that  this  is  one  method  of  insuring  its 
transmission  from  season  to  season. 

Control.  This,  as  well  as  other  shot-hole-producing  fungi,  may 
be  controlled  by  the  use  of  neutral  or  alkaline  dilute  Bordeaux  mix- 
ture, although  the  use  of  Bordeaux  may  be  accompanied  by  in- 
juries to  the  foliage.  Weather  conditions  seem  to  affect  greatly 
its  relations  to  foliage  injuries,  and  this  is  particularly  true  with 
respect  to  the  peach  and  Japanese  plums.  In  any  case,  however, 
thorough  spraying  with  strong  Bordeaux  .should  be  given  in  the' 
early  spring,  whereas  proper  cultivation  should  be  expected  to  de- 
stroy leaves  harboring  the  fungi  from  the  previous  year. 


XL.    FRUIT  SPOT  OF  APPLE  * 
Cylindrosporium  Pomi  Brooks 

BROOKS,  CHARLES.    Fruit  Spot  of  Apple,  a  Morphological  and  Physiological 
Study.    Built.  Torrey  Bot.  Club  35 :  423-456.  pis.  29-35.    1908. 

Occurrence  and  symptoms.  This  disease  is  of  common  occur- 
rence in  New  England  and  is  found  in  New  York,  Michigan, 
Ontario,  and  probably  .in  other  sections  of  the  United  States  and 
Canada.  The  Baldwin  is  especially  susceptible,  but  nearly  every 
New  England  variety  is  more  or  less  affected. 

The  disease  appears  about  the  middle  of  August  as  minute  spots 
or  specks  on  the  surface  of  the  apple.  At  first  these  are  indicated 
merely  by  a  deeper  red  color  of  the  skin,  if  situated  upon  the 
colored  part  of  the  fruit,  or  by  a  green  color,  if  situated  upon  the 
lighter  portion.  As  the  apple  ripens  the  spots  enlarge  and  many 
of  them  become  brown  and  sunken,  giving  the  fruit  an  unsightly 

1  This  account  of  the  fruit  spot  was  kindly  prepared  by  Professor  Charles 
Brooks,  New  Hampshire  College,  Durham,  N.H. 


342  FUNGOUS  DISEASES  OF  PLANTS 

appearance  which  often  greatly  depreciates  its  market  value.    The 
tissue  beneath  the  spots  is  dry  and  brown. 

The  fungus.  The  first  studies  upon  this  disease  seemed  to  indi- 
cate that  it  was  not  produced  by  a  fungus,  but  recent  studies  have 
demonstrated  the  causal  relation  of  a  fungus  which  seems  to  be 
properly  a  species  of  Cylindrosporium,  as  the  title  suggests.  The 
mycelium  is  hyaline,  septate,  and  intercellular.  -Chlamydospores 
are  common  in  the  host  tissue.  In  late  stages  of  the  disease  a 
compact  stroma  develops  just  beneath  the  epidermis  and  finally 


FIG.  165.    CYLINDROSPORIUM  POMI.    (Photographs  by  Charles  Brooks) 
a,  spot  induced  by  inoculation  of  apple  ;  b,  mycelium  in  agar 

breaks  through  it  to  expose  spores  and  sporophores.  The  spores 
are  hyaline,  from  one  to  five  celled,  and  variously  curved  and  con- 
torted. They  are  from  2  to  2.5  ft  in  diameter  and  from  1 5  to  SO/JL  long. 
The  chlamydospores  and  stromata  are  probably  the  agencies  that 
carry  the  fungus  over  the  winter.  Under  ordinary  conditions  of 
preparing  separation  cultures  this  fungus  does  not  readily  grow, 
and  agar  will  ordinarily  dry  out  before  the  fungus  becomes  notice- 
able. On  this  account  it  has  seemed  to  be  a  difficult  organism  to 
isolate.  As  a  matter  of  fact,  however,  under  ordinary  constantly 
moist  conditions  or  in  liquid  media  it  grows  readily.1 

Infection  probably  takes  place  in  July  or  August  when  the  stomata 
are  being  torn  open  and  the  protecting  layers  of  the  lenticels  are 
not  yet  formed,  a  season  when  the  metabolism  of  the  apple  is 
extremely  great  and  the  transpiration  stream  necessarily  large. 

1  The  "  Stippen  "  disease,  long  known  in  Europe  and  now  reported  from  several 
parts  of  the  United  States,  is  regarded  as  entirely  distinct,  and  probably  not  of 
fungous  origin. 


FUNGI  IMPERFECTI 


343 


Control.  This  disease  is  readily  controlled  by  spraying  with 
Bordeaux,  and  weaker  fungicides  are  often  very  effective.  Spray- 
ings made  as  late  as  July  have  been  found  to  entirely  prevent  the 
disease. 

Cylindrosporium  Chrysanthemi  Ell.  &  Dearn1  produces  blotches, 
commonly  termed  blight,  upon  the  leaves  of  some  varieties  of  the 
cultivated  chrysanthemum.  It  may  become  epidemic  at  the  time 
that  the  flowers  are  opening,  apparently  due  to  lessened  vitality  of 
the  lower  leaves. 

XLI.     HEART  ROT  AND  BLIGHT  OF  BEETS 
Phoma  Betce  Frank 

FRANK,  B.  Ueber  die  biologischen  Verhaltnisse  des  die  Herz  und  Trockenfaule 
der  Ruben  erzeugenden  Pilzes.  Ber.  d.  deut.  bot.  Ges.  13:  192-199. 
1895. 

FRANK,  B.    Die  Pilzparasitaren  Krankheiten  der  Pflanzen.    I.e.  pp.  399-403. 

KRUGER,  F.  Die  bis  jetzt  gemacht  Beobachtungen  iiber  Frank's  neuen  Riiben- 
pilz  Phoma  Betae.  Zeitsch.  f.  Pflanzenkr.  4:  13-20.  fig.  i.  1894. 

Habitat  relations.  This  is  one  of  the  most  serious  diseases  of 
the  sugar  beet  in  portions  of  Germany,  Austria,  and  France.  It 
begins  to  manifest  iitself  as  a  rule  in  August  by  blackening  and 
drying  of  the  younger  heart  leaves,  and  later  older  leaves  also  suc- 
cumb, so  that  before  the  period  of  harvesting  all  the  leaves  may 
be  dead  and  merely  the  beet  stub  remain.  In  cases  where  the  beets 
are  grown  for  seed,  the  fungus  may  also  be  found  upon  the  seed 
stalks  and  cases.  It  is  thought  that  this  is  one  means  by  which 
the  fungus  may  pass  over  from  one  year  to  the  next.  From  the 
affected  leaves,  particularly  along  the  course  of  the  fibrovascular 
bundles,  the  browning  and  general  discoloration  of  the  tissues  ex- 
tend into  the  tissues  of  the  root,  and  there  rot  sets  in.  If  the 
disease  begins  early  in  the  season  great  injury  may  be  done.  It  is 
considered  probable  that  this  organism  was  a  chief  agent  in  the 
great  losses  sustained  by  beet  growers  in  Europe  during  the  mid- 
dle of  the  nineteenth  century,  and  the  organism  was  certainly 
again  unusually  prevalent  and  destructive  in  1892-1893.  Frank 
considers  the  Phyllosticta  tabifica  Pril.  &  Del.  to  be  the  same 

1  Halsted,  B.  D.  Recent  Chrysanthemum  Blight.  NJ.  Agl.  Exp.  Sta.  Kept.  15  ; 
365-368.  1894. 


344  FUNGOUS  DISEASES  OF  PLANTS 

organism  as  the  one  here  described.  It  was  also  thought  by  these 
French  observers  that  a  Sphaerella  which  was  found  associated 
with  the  Phyllosticta  might  be  a  perfect  stage  of  the  latter  species.1 

Pycnidia  are  produced  over  practically  all  the  dead  portions  of 
the  plant,  especially,  however,  on  the  leaves  and  leafstalks.  These 
are  small,  more  or  less  spherical  bodies,  with  slightly  depressed 
ostiola ;  pycnidia  measure  up  to  200  ft  in  diameter.  The  fungus 
grows  readily  in  artificial  culture  media,  and  it  has  been  used  by 
Saida  in  some  interesting  experiments  on  the  fixation  of  atmos- 
pheric nitrogen.  Frank  states  that  the  spores  may  remain  alive  in 
moist  soil  throughout  the  winter  without  germinating,  and  then, 
upon  being  placed  in  beet  decoction,  germination  will  promptly 
proceed. 

Control.  Spraying  experiments  have  not  yet  given  complete  satis- 
faction. Care  should  be  taken  to  destroy  such  remains  of  the  previous 
crop  as  is  practicable,  and  the  treatment  of  seed  with  Bordeaux 
mixture  is  desirable  where  disease  abounds.  Fortunately  this  fungus 
has  not  made  its  appearance  in  this  country  up  to  the  present  time. 

XLII.    DRY  ROT  OF  SWEET  POTATO 
Phoma  Batata  Ell.  &  Hals. 

HALSTED,  B.  D.    Some  Fungous  Diseases  of  the  Sweet  Potato.    Dry  Rot. 
N.  J.  Agl.  Exp.  Sta.  Built.  76:   23-25.  fig.  16.    1890. 

This  fungus  is  not  uncommon  in  New  Jersey,  but  it  is  not 
to  be  considered  one  of  the  more  serious  enemies  of  the  sweet 
potato.  A  comparative  study  of  this  species  and  of  forms  upon 
related  hosts  has  not  been  made,  and  it  is  possible  that  it  may  be 
referred  to  a  species  described  earlier.  It  attacks  the  root,  which 
shows  the  effect  of  the  invading  organism  only  by  a  gradual  shrivel- 
ing and  discoloration  of  the  affected  areas.  The  whole  root  may 
become  affected,  and  eventually  dry  and  powdery.  The  pycnidia 
appear  upon  the  surface  in  large  numbers,  and  the  fungus  spreads 
rapidly  during  storage  of  the  roots  under  moisture  conditions. 
The  effects  of  this  fungus  are  frequently  complicated  by  those  of 
other  organisms  attacking  the  root,  especially  certain  forms  pro- 
ducing soft  decay. 

1  Bull.  Soc.  Myc.  de  France  7  :  15-19.    1891. 


FUNGI  IMPERFECTI 


345 


XLIII.    SEEDLING  STEM  BLIGHT  OF  EGGPLANT 
Phoma  Solani  Hals. 

HALSTED,  B.  D.    Some  Fungous  Diseases  of  the  Egg  Plant.    N.  J.  Agl.  Exp. 
Sta.  Kept.  12:  277-279.    1891. 

This  fungus  has  much  the  habit  of  a  damping-off  fungus,  infest- 
ing the  young  seedlings  of  eggplant  near  the  surface  of  the  ground 
before  they  are  removed  from  the  hotbed.  The  diseased  portion 


FIG.  1 66.   BLIGHT  OF  SNAPDRAGON;  PLANTS  AT  THE  RIGHT  AND  LEFT, 
INOCULATED  WITH  PHOMA  HERBARUM  (?)  :  CENTER  PLANT,  CONTROL 

is  first  water-soaked  in  appearance.  Later  this  area  shrivels,  and 
the  diameter  is  much  less  than  that  of  the  healthy  stem  beyond. 
Infected  seedlings  seldom  survive.  The  pycnidia  are  produced 
abundantly  on  the  drying  areas. 


XLIV.    PHYLLOSTICTA 


Phyllosticta  Paviae  Desm.  The  leaf  blotch  caused  by  this  fungus 
is  probably  the  most  important  malady  of  the  horse-chestnut.  The 
irregular  spots  develop  rapidly  as  the  season  advances,  and  the 
larger  part  of  the  leaf  may  become  involved,  from  the  margin  to 


FUNGOUS   DISEASES   OF  PLANTS 


the  midrib,  as  if  sunburned.  Eventually  the  leaves  fall  prematurely 
and  the  vitality  of  the  tree  is  greatly  affected.  The  perithecia  appear 
on  the  upper  surface  of  the  leaves,  but  are  not  usually  present,  at 
least  abundant,  over  the  whole  affected  area. 


FIG.  167.  PHYLLOSTICTA  SOLITARIA:  APPLE  BLOTCH 

Phyllosticta  hortorum  Speg.1  occurs  both  upon  leaves  and  fruit 
of  the  eggplant  (Solanum  Melongena),  producing  upon  the  latter 
soft  spots  which  become  shrunken  and  decayed,  rendering  the  fruit 
worthless. 

Phyllosticta  solitaria  E.  &  E.  A  fungus  producing  a  d'estruc- 
tive  fruit  blotch2  of  the  apple  in  the  South  has  recently  been 
identified  as  the  above  species.  The  disease  is  more  common 
upon  the  light  colored  varieties  of  this  fruit. 

1  Halsted,  B.  D.    Some  Fungous  Diseases  of  the  Egg  Plant.    The  Leaf-Spot 
Fungus.    N.  J.  Agl.  Exp.  Sta.  Kept.  12  :  279-281.    1890. 

2  Scott,  W.  M.,  and  Rorer,  J.  B.    Apple  Blotch.    Bureau  Plant  Ind.,  U.  S.  Dept. 
Agl.  Built.  144:  1-28.  pis.  1-6.    1909. 


FUNGI  IMPERFECT! 


347 


Phyllosticta  maculicola  Hals.1  is  the  cause  of  a  very  common 
leaf  spot  of  several  species  of  Dracaena  and  Cordyline.  The  spots 
are  characterized  by  pale  centers  and  reddish  or  purplish  borders. 
The  disease  is  sometimes  severe  in  greenhouses  where  it  has  long 
been  allowed  to  proceed  unchecked.  It  is,  however,  readily  pre- 
vented by  spraying  with  potassium  sulfide 
solution. 

Phyllosticta  Ampelopsidis  Ell.  &  Mart,  is 
perhaps  closely  related  to  the  fungus  causing 
black  rot  of  the  grape.  It  has  been  injurious 
during  some  seasons  to  the  Boston  or 
Japanese  ivy  (Ampelopsis  Veitchii). 

Phyllosticta  Catalpae  Ell.  &  Mart.2  is 
commonly  found  associated  with  Macro- 
sporium  Catalpce  on  the  leaves  of  several 
species  of  catalpa,  but  it  is  to  the  former 
fungus  that  the  production  of  the  spot  is 
now  ascribed. 

Phyllosticta  Violae  Desm.  occurs  upon 
the  violet  and  the  pansy,  often  causing 
blotch-like,  pale  spots  which  may  result  in 
considerable  injury.  * 

Phyllosticta  Magnolias  Sacc.  produces  a 
very  definite  spot  disease  on  the  leaves  of 
Magnolia  grandiflora  in  Europe. 

Phyllosticta  Pyrina  Sacc.  was  long  sup- 
posed to  be  a  chief  cause  of  the  apple  leaf 
spot  so  common  in  the  United  States. 
Recent  work  indicates  that  the  spot  is  in  general  primarily  due  to 
Sphaeropsis,  and  that  the  Phyllosticta  is  to  be  regarded  as  taking 
a  minor  part  in  the  production  of  the  injury.  In  fact,  the  failure 
of  inoculation  experiments  (see  Sphaeropsis,  p.  352)  appear  to 
demonstrate  that  the  latter  is  saprophytic,  at  least  with  respect 
to  penetration. 

1  Halsted,  B.  D.    Blights  of  Dracaenas.    N.  J.  Agl.  Exp.  Sta.  Kept.  14:  412. 
1893. 

2  Scribner,   F.    L.    Leaf- Spot   Disease  of  Catalpa.    U.  S.  Dept.   Agl.    Kept. 
(1887):  364-369. 


FIG.  168.   DRAC^NA 
LEAF  BLIGHT 


FUNGOUS  DISEASES  OF  PLANTS 

XLV.    BLACK  ROT  OF  SWEET  POTATO 
Sphceronema  fimbriatum  (Ell.  &  Hals.)  Sacc. 

HALSTED,  B.  D.  Some  Fungous  Diseases  of  the  Sweet  Potato.  The  Black 
Rot.  N.  J.  Agl.  Exp.  Sta.  Built.  76:  7-14.  figs.  3-10.  1890. 

HALSTED,  B.  D.,  and  FAIRCHILD,  D.  G.  Sweet-Potatg  Black  Rot.  Journal  of 
Mycology?:  i-ii.  pis.  1-3.  1891. 

The  black  rot  of  the  sweet  potato  is  one  of  the  most  destructive 
diseases  of  this  host,  and  it  is  known  to  occur  from  New  Jersey 
southward  practically  throughout  the  Atlantic  coast  region.  The 
distribution  of  the  fungus,  however,  is  not  completely  known.  The 
disease  may  appear  in  the  seed  bed,  resulting  from  the  use  of 
infested  seed  roots.  The  disease  upon  the  seedlings  is  known  as 
black  shank,  due  to  the  black  spots  or  discolorations  on  the  roots 
and  young  stems.  The  commercial  root  may  be  infested  either 
as  a  result  of  planting  diseased  slips,  or  the  infection  may  be  due 
to  the  presence  of  the  fungus  in  the  soil.  Upon  the  full  grown 
root  the  disease  appears  in  the  form  of  dark  patches  or  decayed 
spots,  which,  upon  more  careful  examination,  and  especially  upon 
removal  of  the  skin,  will  appear  green.  These  spots  vary  in  size 
from  minute  flecks  to  extensive  areas  involving  practically  the  whole 
root.  When  the  roots  are  diseased  there  is  no  appearance  of  the 
vegetative  parts  which  suggests  the  presence  of  the  parasite. 

The  fungus.  The  mycelium  consists  of  septate,  much  branched, 
thick-walled,  olivaceous  hyphae,  which  are  commonly  intercellular. 
The  cells  in  the  region  invaded  are  robbed  of  starch,  and  the  cell 
walls  are  brown  and  often  collapse.  The  fungus  has  many  fruiting 
stages  which  may  be  briefly  referred  to.  Two  kinds  of  conidia  are 
produced,  one  within  the  tissues  consisting  of  simple,  ovate,  green- 
ish cells,  abscised  from  terminal  or  lateral  branches.  Upon  the 
surface  of  the  diseased  area,  or  in  culture,  there  are  also  produced 
minute,  hyaline  conidia.  The  latter  are  developed  endogenously, 
more  or  less  as  described  for  a  similar  phase  in  the  case  of  the 
root  rot  of  tobacco,  Thielavia  basicola.  The  pycnidial  form  is 
produced  within  the  diseased  areas,  and  it  is  also  readily  developed 
in  artificial  cultures.  It  consists  of  a  flask-shaped  pycnidium,  with 
extremely  long  neck.  The  bulbous  portion  is  from  96  to  224  /A  in 
diameter  and  the  neck  from  395  to  608  p  in  length,  and  24-34  /-i 
wide  at  the  base,  tapering  to  12- 14  ft-.  The  method  of  spore 


FUNGI  IMPERFECTI 


349 


production  in  the  pycnidium  has  not  been  clearly  made  out,  but 
the  spores  are  unicellular,  and,  when  mature,  ooze  out  from  the 
tip  of  the  flask-shaped  body,  adhering  in  masses.  They  are  more  or 
less  subglobose  or  oblong,  hyaline,  and  measure  5-9  /a  in  length. 
Upon  immersion  in  water  they  increase  greatly  in  size  and  readily 
germinate. 

When  the  mycelium  has  developed  to  a  considerable  extent  in 
the  root,  sclerotia  of  large  .size  appear.  It  is  believed  that  these 
sclerotia  may  be  properly  a  phase  in  the  life  history  of  this  species, 
and  that  they  may  also  be  important  in  the  perpetuation  or  spread 
of  the  fungus.  This  fungus  will  continue  its  growth  and  develop- 
ment upon  the  stored  roots,  and  also  upon  the  remnants  of  the 
crop  left  in  the  field,  so  that  special  care  must  be  taken  not  only 
with  respect  to  the  quality  of  the  roots  used  at  the  time  of  planting, 
but  also  to  the  prevalence  of  the  disease  during  previous  years  in 
the  fields  where  potatoes  are  to  be  grown. 

The  sunken  area  and  the  greenish  character  of  the  diseased 
portion  enables  one  readily  to  distinguish  the  effects  of  this  fungus 
from  those  produced  by  the  common  black  mold,  Rhizopus  nigri- 
cans  Ehr.,  which  is  the  organism  causing  the  typical  soft  rot  of  this 
crop.  The  latter  disease  is  not  discussed  in  this  work. 

Proceeding  from  the  mycelium  within  the  tissues  the  Sphaero- 
nema  has  been  readily  cultivated  upon  various  artificial  media.  In 
cultures  upon  sweet  potato  agar  a  profuse  mycelium  is  developed. 
The  submerged  hyphae  are  olive  brown  in  color  and  contain  abun- 
dant oil  droplets.  All  three  types  of  spores  are  produced,  aerial 
hyphae  originating  the  endogenous  spores,  and  submerged  sporo- 
phores  producing  the  olivaceous  conidia.  Normal  pycnidia  develop 
in  culture  in  a  week  or  more.  The  disease  has  been  produced  in 
healthy  roots  by  inoculation  with  the  hyaline  conidia  and  with  the 
pycnospores  from  pure  cultures. 

Control.  Seed  roots  for  planting  purposes  should  be  carefully 
selected  and  no  slips  should  be  taken  from  plants  in  the  seed  beds 
showing  disease.  Rotation  of  crops  is  necessary  to  rid  fields  of 
this  fungus.  Apparently  no  experiments  of  interest  have  been 
made  to  determine  the  possibility  of  preventing  the  spread  of  the 
fungus  in  stored  roots.  Nevertheless,  any  conditions  favoring  the 
accumulation  of  moisture  would  be  favorable  to  the  organism. 


350  FUNGOUS  DISEASES  OF  PLANTS 

XLVI.    BLACK  ROT  AND  CANKER  OF  POMACEOUS  FRUITS 
Spharopsis  Malorum  Pk. 

HALSTED,  B.  D.   The  Black  Rot  of  the  Quince.    N.  J.  Agl.  Exp.  Sta.  Built. 

91:  8-10.    1892. 
PADDOCK,  WENDELL.    The  New  York  Apple-tree  Canker.    N.  Y.  Agl.  Exp. 

Sta.  Built.  163:  331-360.  pis.  28-33.    l899- 
PADDOCK,  WENDELL.    Ibid.   (Second  Report)   N.  Y.  Agl.  Exp.  Sta.  Built. 

185:  205-213.    1900. 

Habitat  relations.    Under  the  specific  name  given  above  a  fruit 
decay  of  apples,  quinces,  and' pears  has  become  well  known  although 


FIG.  169.  SPH&ROPSIS  MALORUM  ON  APPLE.    (Photograph  by 
H.  H.  Whetzel) 

not  serious  in  the  United  States.  More  recently  it  has  developed 
that  this  fungus  is  likewise  the  cause  of  an  important  form  of  can- 
ker on  trunks  and  limbs  of  the  same  fruit  trees.  It  has  been  ex- 
tensively studied  only  in  New  York  (Paddock).  Owing  to  the 
occurrence,  however,  of  a  variety  of  cankers  on  the  apple  tree,  this 
one  is  frequently  designated  "  the  New  York  apple  canker." 
This  canker  has  been  found  to  occur  in  many  of  the  northeastern 


FUNGI  IMPERFECTI 


351 


and  northern  central  states,  as  well  as  in  Canada,  and  it  is  not 
improbable  that   it  is  more    or  less  distributed   throughout  the 
country.    Under  other  scientific  names,  moreover,  it  may  also  be 
known    botanically,    at 
least,  in  Europe. 

As  a  rot  of  fruit  the 
fungus  is  more  generally 
known  in  America.  It 
is  a  brown  rot,  begin- 
ning as  a  small  spot,  fre- 
quently near  the  bud  end 
of  the  fruit,  and  spread- 
ing until  the  whole  fruit 
may  be  involved.  There 
is  not  such  characteristic 
shrinkage  of  the  tissues 
as  in  the  case  of  the  bit- 
ter rot.  The  pycnidial 
pustules  may  begin  to 
appear  when  the  spot  is 
only  half  an  inch  in  di- 
ameter, or  they  may  not 
become  evident  until  the 
entire  fruit  is  decayed. 
This  rot  often  attacks 
the  fruit  on  the  trees, 
yet  it  is  far  more  com- 
mon upon  the  neglected 
fallen  fruit  (Fig.  169), 
which  is  a  great  source 
of  danger  to  the  health 
of  the  tree.  In  the  mild- 
est form  the  canker  is  believed  to  cause  merely  a  greater  rough- 
ening of  the  bark,  an  injury  which  may  occur  as  a  single  spot, 
or  which  may  extend  along  the  limb  for  a  distance  of  several  feet. 
In  the  most  serious  cases  it  first  destroys  the  bark,  well-marked 
depressed  areas  being  developed,  about  which  local  swellings  of 
the  limbs  occur,  and  in  these  affected  areas  the  wood  at  the  center 


FIG.  170.   THE  SPH^EROPSIS  CANKER  OF  APPLE 
(Photograph  by  H.  H.  Whetzel) 


352  FUNGOUS  DISEASES  OF  PLANTS 

may  be  exposed,  or  extensive  wounds  may  result.  The  disease  is 
more  common  upon  the  larger  limbs  of  older  trees,  but  trunks  and 
twigs  are  not  exempt,  and  young  trees  may  suffer.  When  complete 
girdling  results,  the  limb  is  killed,  yet  serious  consequences  may 
gradually  develop  without  girdling.  Fig.  1 70  shows  an  early  stage 
of  this  canker. 

Infection  is  probably  most  frequent  in  the  spring.  It  is  believed 
upon  good  evidence  that  the  worst  wounds  occur  only  when  the 
fungus  gains  entrance  to  the  edge  of  the  wood  through  wounds. 
Trees  which  sunscald  badly  on  the  parts  exposed  to  the  direct 
rays  of  the  southwest  sun  are  as  a  rule  subsequently  infested  with 
canker.  In  New  York  the  Spitzenburg  and  Twenty  Ounce  are 
mentioned  as  the  most  susceptible  varieties  of  apple  to  the  limb 
canker,  while  Baldwin,  Wagoner,  Greening,  and  King  follow  in 
the  order  given  ;  the  Tallman  Sweet  was  reported  practically 
resistant.  The  susceptible  varieties  of  pear  are  not  known.  In 
some  cases,  at  least,  the  body  blight  of  pear  is  also  to  be  attributed 
to  this  canker  organism. 

Infrequently  a  Sphaeropsis  has  been  found  upon  the  leaves  of 
the  pear,  and  this  form  appears  to  be  similar  to  the  canker  fungus.1 
It  is  thought  that  general  neglect,  crowding,  lack  of  pruning, 
etc.,  encourage  the  canker,  although  it  may  appear  in  vigorous 
orchards.  There  would  appear  to  be  absolutely  no  doubt  that  the 
rot  of  apples,  pears,  and  quinces  is  due  to  the  one  fungus.  Trans- 
fers of  this  organism  are  readily  made.  Paddock  made  many  pure 
cultures  as  well  as  many  transfers  of  the  canker  strains  to  fruits 
and  vice  versa,  also  to  a  variety  of  other  hosts.  The  inoculation 

1  From  extensive  experiments  made  during  1907  by  Scott  and  Rorer,  it  has 
been  demonstrated  that  the  common  leaf  spot  of  the  apple,  as  it  occurs  east  of 
the  Rocky  Mountains,  is  also  generally  traceable  to  Sphczropsis  Malorum  Pk.  as 
a  primary  cause.  The  other  fungi  which  have  been  associated  with  the  apple 
spot,  such,  for  instance,  as  Phyllosticta  Pyrina  Sacc.  and  Phyllosticta  limitata  Pk., 
have  not  been  found  to  induce  leaf  spots  upon  inoculation.  From  young  spots 
the  Sphaeropsis  colonies  are  constantly  plated  out,  and  the  other  fungi  mentioned 
were  only  present  during  the  later  stages  of  the  disease.  Moreover,  inoculation 
experiments  with  the  former  have  almost  invariably  yielded  positive  results 
within  from  five  to  ten  days.  These  observers  are  of  the  opinion,  therefore,  that 
neither  Phyllosticta  nor  other  forms  which  may  be  found  upon  those  spots  are  of 
any  special  importance  in  the  apple  orchard.  (Scott,  W.  M.,  and  Rorer,  J.  B., 
Apple  Leaf- Spot  caused  by  Sphaeropsis  Malorum.  Bureau  Plant  Industry,  U.  S. 
Dept.  Agl.  Built.  121 :  47-54.  1908.) 


FUNGI  IMPERFECTI 


353 


experiments  suggest  that  Spharopsis  Mali  (West)  Sacc.  on  bark, 
Sph<zropsis  cinerea  (C.  &  E.)  Sacc.,  and  Sphceropis  Malonim  Pk. 
are  properly  the  same  fungus.  Until,  however,  more  careful  com- 
parisons shall  have  been  made,  we  may  continue  to  refer  to  this 
disease-producing  fungus  as  Sphceropsis  Malonim.  It  may  be, 
moreover,  that  it  occurs  upon  many  other  hosts. 

The   fungus.    The    mycelium    is    sooty   brown    or   olivaceous 
within  the  tissues.    It  penetrates  the  bark  readily  but  may  not 


FIG.  171.  SPHCEROPSIS  MALORUM  :  MATURE  PYCNIDIUM.    (Photograph 
of  a  drawing  by  F.  C.  Stewart) 

extend  far  into  the  wood.  The  pycnidia  are  erumpent,  usually  sur- 
rounded by  a  broken  epidermis  (Fig.  i/i),  and  they  appear  in 
cross  section  somewhat  depressed-conical  at  the  apex.  The  spores 
are  oblong-elliptical,  brown,  and  usually  about  twice  as  long  as 
broad,  measuring  in  general  22-32  x  10-14/11.  It  has  been  found 
that  the  average  sizes  of  the  spores  of  the  forms  on  apple,  pear, 
and  quince  vary  according  to  the  host  and  part  attacked.  The  most 
noteworthy  difference  is  that  upon  the  limbs  the  spores  are  smaller 
than  on  the  fruits.  The  spores  seem  to  retain  their  vitality  for  a 
considerable  period  of  time,  having  been  germinated  after  being 
stored  for  a  year  in  the  laboratory.  .On  agar  the  fungus  develops 


354 


FUNGOUS  DISEASES  OF  PLANTS 


effuse  colonies,  the  aerial  portions  of  which  are  at  first  gray,  be- 
coming darker  with  age.  The  pycnidia  may  sometimes  be  pro- 
duced in  agar  and  also  upon 
various  solid  media  in  tube 
cultures. 

Control.  Preventive  meas- 
ures have  not  been  carefully 
worked  out.  Under  ordinary 
circumstances  orchards  in 
good  condition  will  suffer  least. 
Advantage  may  also  be  de- 
rived from  treating  the  limbs 
and  trunk  thoroughly  with  any 
"  cleaning  up.  "  washes,  or  with 
Bordeaux  mixture.  For"  varie- 
ties susceptible  to  sunscald, 
after  which  the  canker  may  be 
common,  it  is  recommended  to  give^a  \vinter  spraying  with  white- 
wash. Pruning  and  scraping  may  also  be  required,  and  along  with 
this  the  wholesale  destruction  of  affected  limbs  or  fruit. 


FIG.  172.   ISOLATION  CULTURE  OF 
SPXJEROPSIS  MALORUM 


XLVII.    RASPBERRY  CANE  BLIGHT 
Coniothyrium  Fuckelii  Sacc. 

STEWART,  F.  C.  Raspberry  Cane  Blight  and  Raspberry  Yellows.  N.  Y.  (Geneva) 
Agl.  Exp.  Sta.  Built.  226:  331-366.  pis,  1-6.    1902. 

Habitat  relations.  This  is  a  fungus  which,  as  a  disease-produc- 
ing organism,  has  been  known  only  a  few  years ;  and  it  may  be 
that  the  species  is  new.  The  botanical  name  given  above  is  applied 
to  a  fungus  which  was  described  as  occurring  on  a  variety  of  shrubs 
and  trees,  the  genus  Rubus  being  among  the  hosts  mentioned. 
Stewart  and  Eustace  have  tentatively  referred  the  fungus  caus- 
ing raspberry  cane  blight  to  this  variable  species. 

The  cane  blight  is  a  widespread  disease  in  New  York  state, 
and  doubtless  quite  common  throughout  the  country  upon  rasp- 
berries. It  is  essentially  a  wilt  disease  (Fig.  173),  and  the  principal 
damage  results  to  the  fruiting  canes.  In  some  instances,  however, 
young  canes  may  be  killed  during  the  first  season  of  growth. 


FUNGI  IMPERFECTI 


355 


FIG.  173.    RASPBERRY  CANE  BLIGHT.    (Photograph  by  F.  C.  Stewart) 

Stewart  states  : 

The  whole  cane  may  be  involved  or  only  a  portion  of  it.  Often  a  single 
branch  is  killed  while  the  remainder  of  the  cane  continues  alive  and  appar- 
ently normal.  In  the  majority  of  cases  only  a  part  of  the  cane  dies.  With 
black  caps  the  disease  frequently  starts  in  the  old  stub  left  in  pruning.  From 


356  FUNGOUS  DISEASES  OF  PLANTS 

this  point  it  gradually  works  downward,  killing  first  the  uppermost  branch, 
then  the  next  lower  one,  and  so  on  until  by  the  close  of  the  berry  harvest  one- 
half  of  the  cane  or  more  may  be  dead.  On  black  caps  the  disease  also  shows 
a  tendency  to  work  down  one  side  of  the  cane,  killing  the  bark  and  discolor- 
ing the  wood  on  that  side,  while  on  the  other  side  the  bark  remains  green. 

The  disease  occurs  both  upon  black  and  red  varieties  of  the 
raspberry,  and  it  is  thought  that  it  may  also  injure  dewberries. 
Cuthbert,  Marlboro,  Ohio,  Gregg,  Kansas,  Superlative,  I.X.L., 
and  Pride  of  Geneva  are  varieties  of  raspberry  which  have  been 
found  to  have  been  much  injured  in  New  York,  while  Columbian 
has  proved  notably  resistant.  The  amount  'of  damage  which  may 
be  done  when  nonresistant  sorts  are  grown  is  commonly  estimated 
at  from  one  fourth  to  two  thirds  of  the  crop.  The  disease  doubt- 
less spreads  most  rapidly  during  moist,  warm 
summers,  but  its  destructive  effects  upon  the 
fruit  crop  are  particularly  noted  during  a  sea- 
son of  drought.1 

The  fungus.    By  the  time  that  a  cane  is  com- 
pletely wilted  there  may  be  found  at  the  base 
of  the  wilted  portion  a  short  area  dead  and 
discolored,  in  which  appear  the  pycnidia.  When 
FIG.  174-   CONIOTHY-     expelled  from  the  pycnidia  the  spores  form 

RIUM FUCKELH.  (After 

Stewart)  brownish  patches  on  the  dead  bark,  or  the 

dying  canes  might  have  a  smutty  appearance 
from  the  presence  of  numerous  spores.  Viewed  singly  the  spores 
are  very  lightly  colored,  but  in  mass  the  brown  color  is  pronounced. 
The  spores  measure  2.4-5  X  2~3-5  P  (Fig.  174).  Pure  cultures  of 
this  fungus  were  obtained,  but  a  description  of  growth  characters  has 
not  yet  appeared.  Results  from  most  carefully  conducted  inocula- 
tion experiments  made  from  pure  cultures  have  clearly  demon- 
strated the  parasitic  nature  of  the  disease,  and  the  independence 
of  Coniothyrium  in  producing  it. 

1  Clinton  thinks  (Conn.  Agl.  Exp.  Sta.  Rept.  (1906) :  321-324)  that  the  raspberry 
cane  blight  fungus  gains  entrance  through  the  flowers  and  young  fruit,  the  spores 
apparently  being  spread  by  bees  and  other  insects.  In  Connecticut  the  black 
cap  varieties  have  been  more  susceptible,  special  complaint  having  been  made  of 
serious  injury  to  the  Farmer,  Cumberland,  and  Kansas.  It  has  also,  however,  in- 
jured red  varieties  and  occurs  on  wild  black  raspberries  in  the  same  region.  He 
presents  no  further  proof  of  the  connection  with  Leptosphaeria,  but  refers  the 
fungus  to  that  genus  under  the  name  Leptosphceria  Coniothyrium  (Fckl.)  Sacc. 


FUNGI  IMPERFECTI 


357 


Control.  It  appears  that  the  only  practical  methods  of  prevent- 
ing this  disease  are  to  obtain  healthy  plants  at  the  outset,  to  avoid 
planting  where  raspberries  or  other  related  plants  have  grown,  and 
to  remove  and  burn  old  canes  as  promptly  as  possible.  The  results 
with  spraying  have  not  thus  far  been  successful. 


XLVIII.    ROSE  LEAF  BLOTCH 
Actinonema  Rosa  (Lib.)  Fr. 

COBB,  N.  A.   Black  Spot  of  the  Rose.   Dept  Agl.  N.  S.  Wales.   Miscel.  Publ. 

(2d  Ser.)  666:  2-27.    ///.    1904. 
SCRIBNER,  F.  L.    Black  Spot  of  Rose  Leaves.    U.  S.  Dept.  Agl.  Rept.  (1887): 

366-368.  pis.  8,  9. 

The  rose  leaf  blotch,  or  spot,  is  perhaps  the  most  common  and 
injurious  rose  fungus  aside  from  the  powdery  mildew  (p.  224).  This 
disease  is  characterized  by  more 
or  less  irregular  brown  spots,  fairly 
well  defined,  on  the  upper  sur- 
faces of  the  leaves  (Fig.  175), 
varying  from  a  few  millimeters  in 
diameter  to  areas  covering  more 
than  one  half  the  entire  leaflet. 
In  this  darkened  area  there  are 
distributed  a  small  number  of  pyc- 
nidia,  producing  numerous,  ellip- 
tical, two-celled,  hyaline  conidia. 
This  spot  may  be  controlled  by 
the  use  of  any  standard  copper 
spray,  but  it  is  not,  of  course,  de- 
sirable to  spray  for  a  few  weeks 
preceding  the  blossoming  period. 
Control  measures  should  there- 
fore look  to  preventing  the  dis- 
ease from  securing  a  start  previous  to  the  blossoming  season. 

There  is  considerable  difference  in  the  susceptibility  of  the  dif- 
ferent host  varieties.  As  a  rule  the  bushy  sorts  are  more  severely 
injured  and  the  climbing  roses  are  often  immune.  If  cuttings  are 
selected  from  healthy  plants,  even  susceptible  varieties  may  be 
generally  propagated  with  little  fear  of  serious  trouble. 


FIG.  175.   LEAF  BLOTCH  OF  ROSE 


358  FUNGOUS  DISEASES  OF  PLANTS 

XLIX.    LEAF  SPOT  OF  THE  PEAR 
Septoria  Pyricola  Desm. 

DUGGAR,  B.  M.    Some  Important  Pear  Diseases.    Leaf  Spot.    Cornell  Agl. 
Exp.  Sta.  Built.  145:  59?-6n.  figs.  I57~l65'    l898- 

The  leaf  spot  of  pear  is  a  disease  which  may  be  readily  dis- 
tinguished from  the  leaf  blight  subsequently  described.  It  occurs 
throughout  the  eastern  United  States  as  an  important  fungus,  both 


FIG.  176.   LEAF  SPOT  OF  PEAR 

in  orchards  and  nurseries.    It  is  probably  found  throughout  North 
America  and  is  reported  from  various  parts  of  Europe. 

The  leaf  spot  fungus  is  confined  to  the  leaves,  and  in  orchards 
the  chief  injury  to  trees  may  be  the  reduced  vigor  for  the  next 
season,  due  to  premature  defoliation.  It  is  rather  remarkable  that 
while  seedling  apple  stock  in  a  nursery  may  show  leaf  blight  to  a 
considerable  extent,  adjacent  plots  of  budded  plants  may  be  seri- 
ously injured  by  the  leaf  spot.  The  budded  stock  of  the  second 
year  usually  suffers  more  severely,  particularly  since  it  is  generally 
less  cultivated  after  the  first  season.  In  the  state  of  New  York 
most  of  the  standard  varieties  may  be  attacked.  Bosc,  Anjou, 
Clairgeau,  Seckel,  Bartlett,  etc.,  may  be  considerably  injured,  but 
Flemish  Beauty,  Duchess,  and  Winter  Nellis  are  more  resistant. 


FUNGI  IMPERFECTI  359 

The   Kieffer  is  practically  exempt.    In  any  case,   however,   the 
fungus  may  be  readily  controlled  with  Bordeaux. 

The  spots  on  the  leaves  are  few  or  numerous,  angular,  and  the 
size  varies  greatly  with  the  variety.  Three  fairly  well  differentiated 
zones  of  color  are  shown  in  an  affected  spot :  at  the  center  it  is 
ashen  gray,  and  within  this  area  appear  on  either  surface  the  minute 
pycnidia ;  the  next  outer  zone,  or  area,  is  brown,  or  black  in  very 
young  leaves ;  and  surrounding  this  second  there  may  be  an  area 


FIG.  177.    DILUTION  CULTURE  OF  SEPTORIA  PYRICOLA 

which  is  purplish  in  color  (Fig.  176).  These  color  details  are  lost 
in  very  old  leaves,  but  the  black  papillae  indicating  the  pycnidia 
then  show  up  clearly.  At  maturity  the  spores  may  ooze  out  in  dark 
uniform  cirrae.  In  cross  section  the  pycnidium  is  clearly  ovate  in 
form.  The  wall  is  made  up  of  several  layers  of  dark  cells,  and  the 
hyaline  conidiophores  arise  from  an  inconspicuous  inner  layer 
(Fig.  178).  The  spores  are  flexuous  and  quite  constantly  two- 
septate,  measuring  about  60  x  3-4  /*.  The  mycelium  is  intercel- 
lular, brownish,  and  may  be  detected  within  the  tissues  at  some  little 
distance  from  the  perithecium.  The  spores  germinate  readily  in 


36° 


FUNGOUS  DISEASES  OF  PLANTS 


nutrient  media, 
germ  tubes  being 
pushed  out  from 
either  end  or  from 
the  middle  (Fig. 
179).  This  fungus 
has  been  readily 
cultivated  upon 
bean  stems  and 
pear  twigs,  and  I 
have  reported  the 
growth  as  follows : 

Here  the  fungus 
grew  slowly  at  first, 
producing  after  sev- 
eral weeks  the  pyc- 

FIG.  178.  SHPTORIA  PYRICOLA  :  SECTION  OF  PYCNIDIUM      nidia  of  the  SePtoria- 

After  several  trans- 
fers this  fungus  grows  quite  luxuriantly  on  bean  pods  or  stems,  as  seen  in  fig- 
ure .  .  .  ,  producing  the  pycnidia  in  a  short  time,  and  the  pycnidia  are  then  not 
so  definite  in  form  but  formed  of  a 
very  loose  stromatic  mass.  The  sub- 
merged hyphae  are  dark  in  color,  while 
the  aerial  growth  is  dense  and  white, 
except  the  stromatic  mass  inclosing 
the  pycnidium.  I  have  had  cultures 
for  eighteen  months;  and  although 
they  have  been  subjected  to  various 
climatic  conditions,  nothing  of  further 
interest  has  as  yet  come  from  them. 
In  nature  the  fungus  is  being  closely 
watched  for  other  stages,  but  I  can 
say  nothing  definite  upon  this  point 
at  present,  although  other  fungi  have 
been  found  on  the  old  leaves.  FIG.  179.  SEPTORIA  PYRICOLA:  GER- 

MINATING  SPORES 
Control.    This    fungus  has 

been  readily  controlled  hi  the  orchard  by  the  use  of  standard  Bor- 
deaux mixture  applied  as  for  pear  scab.  Where  vigorous  nursery 
stock  would  be  produced,  it  is  necessary  to  spray  every  season ; 
but  a  single  application,  after  the  first  flush  of  growth,  is  often 
sufficient. 


FUNGI  IMPERFECTI  361 

L.    LATE  BLIGHT  OF  CELERY 
Septoria  Petroselini  Desm.,  var.  Apii  Br.  &  Cav. 

BEACH,  S.  A.    Celery  Septoria.    N.  Y.  Agl.  Exp.  Sta.  Built.  51:    137-141. 

1893. 
DUGGAR,  B.  M.    Late  Blight  of  Celery.    Cornell  Agl.  Exp.  Sta.  Built.  132 : 

206-220.  figs.  48-60.    1897. 

Habitat  relations.  The  late  blight  of  celery  is  a  comparatively 
recent  disease  in  the  United  States,  and  in  Europe  it  has  not  been 
considered  a  serious  celery  malady.  It  is  most  injurious  as  a  rule 
during  the  early  autumn,  although  a  few  spots  of  this  disease  may 
be  seen  at  any  time  during  the  summer  where  it  is.  at  all  prevalent. 
The  spots  are  irregular  in  outline  and  of  a  rusty  brown  color.  How- 
ever, when  the  conditions  are  most  favorable  for  the  development 
of  the  disease,  the  fungus  may  spread  over  the  whole  surface  of 
the  leaflets  without  the  formation  of  characteristic  spots. 

The  late  blight  is  destructive  in  the  field  until  the  plants  are 
"  lifted."  It  may  also  extend  its  injuries  to  the  storage  coop  or 
cellar.  The  conditions  in  the  storage  cellar  may  be,  during  warm 
days  of  early  winter,  most  favorable  for  the  spread  of  the  fungus. 
In  a  moist,  poorly  ventilated  cellar  I  have  found  the  pycnidia  of 
this  fungus  over  the  surfaces  of  entire  leaves,  and  the  whole  plant 
wilted  as  a  result. 

The  fungus.  The  pycnidia  of  this  fungus  are  evident  soon  after 
the  spots  turn  brown,  —  as  dark  papillae  more  or  less  in  the  center 
of  the  affected  areas.  The  spores  are  slightly  curved  and  septate, 
the  septa  being  usually  readily  seen  only  by  the  use  of  stains. 

Fresh  spores  germinate  in  a  few  hours  in  nutrient  agar,  and 
transfers  may  be  made  to  bean  stems  and  any  other  solid  media 
for  a  more  profuse  mycelial  development.  Moreover,  on  solid 
media  mature  pycnidia  may  be  secured  within  a  few  weeks.  They 
develop  superficially,  and  are  then  composed  of  loosely  woven 
brown  hyphae.  The  mycelium  is  entirely  distinct  from  that  of 
Cercospora  Apii. 

Control.  In  the  field  Bordeaux  or  ammoniacal  copper  carbo- 
nate may  be  used  as  a  spray,  but  in  the  storage  cellar  it  is  necessary 
to  pay  special  attention  to  all  matters  of  sanitation.  When  the 
disease  is  abundant  in  the  field,  additional  risk  is  taken,  of  course, 
by  placing  the  crop  in  storage. 


362 


FUNGOUS  DISEASES   OF  PLANTS 


LI.    SEPTORIA:    OTHER   SPECIES 


Septoria   Lycopersici   Speg.,  leaf  blight  of  the  tomato.   The 

tomato  is  attacked  by  several  leaf  fungi  which  may  become  destruc- 
tive, and  of  these  fungi  the  one  most  injurious  throughout  the 
range  of  tomato  culture  is  the  organism  causing  what  is  known  as 
leaf  blight.  The  leaves  are  the  parts  most  severely  affected,  and  on 
these  parts  appear  numerous  small  angular  spots  pale  in  the  centers 


FIG.  180.   TOMATOES  DEFOLIATED  BY  THE  LEAF  BLIGHT  FUNGUS 
(Photograph  by  H.  H.  Whetzel) 

and  with  colored  borders.  The  affected  leaves  have  a  tendency  to 
curl  dorsally  throughout  their  length,  eventually  drying  and  falling. 
Petioles  and  twigs  may  also  be  affected,  and  small,  elongate,  dark 
spots  may  appear  on  the  fruit. 

The  pycnidia  are  found  on  the  upper  surfaces  of  the  leaves  in 
the  larger  spots.  It  is  probable  that  the  fungus  passes  the  winter 
in  the  old  leaves  and  other  refuse. 

The  use  of  Bordeaux  mixture  during  the  early  part  of  the 
season  has  generally  resulted  in  successful  prevention. 


FUNGI  IMPERFECTI 


363 


Septoria  Ribis  Desm.1  is  common  upon  various  species  of  Ribes. 
With  respect  to  the  economic  hosts  many  varieties  of  both  currants 
and  gooseberries  are  subject  to  attack.  Large  spots  with  pale 
centers  and  brown  borders  are  produced  (Fig.  181).  These  are 
readily  distinguished  from  those  produced  by  the  anthracnose  (cf. 
Fig.  79)  by  the  large  size,  the  well-defined  outline,  and  the  pale 
central  dead  area.  The  pycnidia  are  found  in  small  groups  at  the 
centers  of  the  older  spots. 
They  are  subspherical,  and, 
when  approaching  maturity, 
crowded  with  spores  arising 
from  short  filiform  conidio- 
phores.  The  conidia  are  long- 
filiform  and  measure  50-60  x 

3-4  /*. 

Septoria  Rubi  West  pro- 
duces numerous  small  spots, 
usually  pale  in  the  centers  with 
colored  borders,  on  the  leaves 
of  various  species  of  Rubus, 
both  blackberries  and  rasp- 
berries.2 The  fungus  has  been 
reported  from  many  sections 
of  the  world,  and  is  doubtless  very  generally  distributed.  Pyc- 
nidia are  developed  in  the  center  of  the  larger  spots,  and  these 
give  rise  to  long  tapering  spores,  40-50^,  ordinarily  twice  or 
more  septate  by  rather  indistinct  divisions. 

Septoria  consimilis  E.  &  M.  The  lettuce  leaf  spot,  caused  by 
this  fungus,  is  prevalent  on  garden  lettuce,  particularly  during  the 
latter  part  of  the  season.  It  is  perhaps  the  chief  "  spot "  fungus 
of  this  plant,  but  may  be  held  in  check  by  the  immediate  destruc- 
tion of  the  discarded  and  seeded  plants  in  the  field  at  the  close  of 
the  season. 

Septoria  Dianthi  Desm.  produces  small  brown  spots  upon  the 
leaves  and  internodes  of  the  carnation.  The  leaves  are  often  bent 

1  Pammel,  L.  H.    Spot  Diseases  of  Currants  and  Gooseberries.   Iowa  Agl.  Exp. 
Sta.  Built.  13  :  67-70.  figs.  13-16.    1891. 

2  Ohio  Agl.  Exp.  Sta.  Built.  4  (6) :  126.    1891-. 


FIG.  181.   LEAF  SPOT  OF  CURRANTS 
(Photograph  by  F.  C.  Stewart) 


364 


FUNGOUS  DISEASES  OF  PLANTS 


or  distorted.    This  disease  is  not  likely  to  be  serious  where  proper 
ventilation  and  subirrigation  are  provided  for. 

Septoria  Chrysanthemi  Cav.  may  become  a  serious  pest  upon 
the  maturing  leaves  of  the  cultivated  chrysanthemum. 


LII.    CURRANT   CANE   BLIGHT 
Dothiorella 

This  disease  appears  to  be  most  abundant  in  the  Hudson 
Valley  in  New  York.  It  has,  however,  been  found  in  other 
sections,  though  not  destructive.  The  affected  canes  are  wilted 
and  killed  during  midsummer.  The  disease  is  probably  more 

easily  seen  during  a  dry  period  on  ac- 
count of  the  fact  that  when  the  water 
supply  is  abundant,  it  may  not  be 
noticeable  during  the  growing  season. 
The  fungus  producing  this  disease  has 
been  isolated  from  both  the  diseased 
wood  and  pith,  and  upon  infection  is 
capable  of  reproducing  the  disease.  Sev- 
eral fruiting  stages  have  been  found,  at 
least  one  of  which  is  unquestionably  a 
stage  in  the  life  cycle  of  this  fungus.  It 
has  been  difficult  to  identify  all  of  the 
spore  forms  with  certainty,  but  the  pyc- 
nidial  stage  would  be  considered  a  species 
of  Dothiorella  (Fig.  182).  Successful 
infection  experiments  with  mycelium 
obtained  from  germinating  pycnospores 
have  been  made.  The  relationship  of 
this  fungus  to  an  ascogenous  stage 
sometimes  associated  with  it,  or  follow- 
ing it,  upon  the  dead  canes  has  been 
under  careful  study,  but  has  not  yet 
been  reported.  The  fungus  grows  read- 
ily upon  any  of  the  solid  nutrient  media, 
KIU..SS.  DOTK™AON  Producing  a  considerable  gray-green 
CURRANT  CANES  mycelium. 


FUNGI  IMPERFECTI 


365 


LIIL    LEAF  BLIGHT  OF  PEAR  AND  QUINCE 
Entomosporium  maculatum  Lev. 

DUGGAR,  B.  M.    Some  Important  Pear  Diseases.    II.    Leaf  Blight.    Cornell 

Agl.  Exp.  Sta.  Built.  145:  611-615.    l898- 
FAIRCHILD,  D.  G.    Experiments  in   Preventing  Leaf   Diseases  of  Nursery 

Stock  in  Western  New  York.    N.  Y.  Agl.  Exp.  Sta.  Kept.  11 :  642-652. 

1892.  (Also,  Journ.  Myc.  8:  338-351.) 
SCRIBNER,  F.  L.    Leaf-Blight  and  Cracking  of  the  Pear.    U.  S.  Dept.  Agl. 

(1888):  357-364. 


Habitat  relations.  The  leaf  blight  of  the  pear  and  quince  has 
been  observed  in  this  country  as  well  as  in  Europe  for  many  years  ; 
it  has  also  received  considerable  attention  at 
various  agricultural  experiment  stations  in  pear- 
producing  regions.  In  New  York  it  is  most 
abundant  apparently  in  the  Hudson  Valley,  and 
in  general  it  would  seem  to  be  more  injurious 
in  states  in  the  Appalachian  region.  Nearly 
all  varieties  of  pear  are  affected,  but  Duchess 
and  Kieffer  are  perhaps  the  most  resistant  of 
those  ordinarily  grown.  Moreover,  in  different 
regions  of  the  Atlantic  states  there  seems  to  be 
a  difference  in  the  susceptibility  of  varieties. 
Considerable  damage  may  also  be  done  in  the 
nurseries  to  seedling  pears,  although  grafted 
stock  is  far  more  subject  to  the  leaf  spot  than 
to  the  leaf  blight.  Root  suckers  on  seedling 
pears  throughout  the  country  are  very  generally 
injured.  The  spots  are  sometimes  noticed  on 
the  tips  of  young  branches,  and  it  has  been  very  definitely  shown 
that  in  such  situations  the  fungus  may  readily  pass  the  winter. 
The  effect  of  the  disease  upon  seedlings  is  to  harden  the  wood 
early  and  prevent  the  best  results  from  budding. 

Symptoms.  The  spots  produced  by  this  fungus  are  particularly 
evident  on  the  upper  surfaces  of  the  leaves,  occurring  first  as  small 
discolored  areas  which  become  dull  red  at  the  center,  with  dark 
borders.  They  are  more  or  less  circular  in  outline,  but  they  may  be 
closely  clustered  and  considerably  confluent.  In  severe  attacks  the 
leaves  may  become  yellow  or  brown,  and  they  readily  fall.  This 


FIG.  183.   ENTOMO- 
SPORIUM ON   PEAR 
(P  h  otograph  by 
Geo.  F.  Atkinson) 


366 


FUNGOUS  DISEASES  OF  PLANTS 


disease  is  distinguished  from  the  leaf  spot  by  smaller  spots  more 
colored  when  young  and  more  nearly  circular.  They  are  also 

less  clearly  defined  on  the  under 
surfaces. 

The  blight  also  attacks  the  fruit. 
In  this  case  the  spots  are  at  first 
red  but  later  darker  in  color.  The 
drying  of  the  surface  layers  accom- 
panying the  effects  of  this  disease 
may  cause  a  cracking  very  much 
as  in  the  case  of  pear  scab. 

The  fungus.  The  larger  spots 
of  the  leaf  blight  will  generally 
show  at  the  time  of  leaf  fall  one 
dark  papilla  in  the  center  of  each. 
This  papilla  is  an  indication  of 
an  acervulus,  or  spore-producing 
stroma.  The  mycelium  from  which 
this  stroma  originates  penetrates 
the  epidermal  layer  and  also  to 
some  extent  the  hypodermal  tis- 
sues, and  the  affected  region  shows  a  general  collapse  of  the 
cells.  From  the  subcuticular  stroma  there  are  produced  on  minute 
conidiophores  numerous  "insect-like"  spores  (Figs.  185,  186).  The 
spores  germinate  readily  and  the  fungus  is  thereby  spread  during 
the  same  season. 
Various  authors 
have  described  what 
is  supposed  to  be  a 
perfect  stage  of  this 
fungus.  Sorauer1 

FIG.  185.    ENTOMOSPORIUM  MACULATUM 

has  referred  the 

ascogenous  stage  to  Stigmatea  Mespili.  Atkinson  2  has  found  this 
fungus  on  wintered  leaves  of  the  quince  and  has  considered  it  to 
be  a  member  of  the  genus  Fabraea. 

Control.    Experiments   upon    nursery   stock    have    shown    that 
Bordeaux  mixture  of  any  standard  strength  may  be  used  success- 

1  Pflanzenkrankheiten,  I.e.  (cf.  p.  371).      2  Garden  and  Forest  10  :  73-74.    1897. 


FIG.  184.   ENTOMOSPORIUM  ON 

QUINCE.   (Photograph  by  H.  H. 

.  Whetzel) 


FUNGI  IMPERFECTI  367 

fully  as  a  preventive.  Five  or  more 
sprayings  have  been  profitable  upon 
American,  French,  and  Japanese 
stocks,  although  this  has  not  afforded 
complete  protection.  Spraying  as  for 
the  pear  scab  is  advised  when  this 
disease  becomes  a  matter  of  suffi- 
cient economic  importance  in  the 

PIG.  186.    SPORES  OF  THE 
orchard.  ENTOMOSPORIUM 

LIV.     SOOTY  BLOTCH  AND  FLY  SPECK  OF  THE  APPLE  AND 
OTHER  PLANTS l 

Leptothyrium  Pomi  (Mont.  &  Fr.)  Sacc. 

CLINTON,  G.  P.    Notes  on  Parasitic  Fungi.   Fly  Speck.   Sooty  Blotch.    Conn. 

Agl.  Exp.  Sta.  Rept.  (1903):  299-302. 
POWELL,  G.  H.    A  Fungous  Disease  of  the  Apple.    Garden  and  Forest  9 : 

474-475.. 
SELBY,  A.  D.    Sooty  Fungus  and  Fly  Speck  Fungus.    Ohio  Agl.  Exp.  Sta. 

Built.  79:    133-134. 
STURGIS,  W.  C.    On  the  Cause  and  Prevention  of  a  Fungous  Disease  of  the 

Apple.    Conn.  Agl.  Exp.  Sta.  Rept.  21:   171-175. 

According  to  the  unpublished  observations  of  Floyd  the  sooty 
^lotcrTand  fly  speck  are  apparently  stages  of  the  same  fungus. 
They  are  almost  invariably  associated  upon  the  host  (Fig.  187),  but 
may  occupy  distinct  areas  upon  the  same  portion  of  the  plant. 
They  seem  to  occur  upon  the  fruit  of  the  apple  throughout  the 
limits.jOf  its  culture.  A  sooty  blotch  and  a  fly  speck  are  also  found 
upon  the  pear,  and  along  a  roadside  near  Columbia,  Mo.,  there 
were  found'7 more  than  twenty-five  hosts  affected  by  what  was 
apparently  the  same  fungus.  These  plants  were  all  woody  in  tex- 
ture, and  the  fungus  occurred  generally  on  the  younger  twigs 
and  petioles.  The  forms  upon  these  hosts  may  be  provisionally 
referred  to  as  one  fungus.  Observation  indicates  that  the  organ- 
fesp,.  is  most  abundant  under  conditions  of  considerable  moisture, 
felf  shade,  and  abundant  dust.  The  market  value  of  apples  is 
affected  by  the  discolorations  which  result. 

1  For  the  material  of  this  account  I  am  very  largely  indebted  to  unpublished 
data  kindly  furnished  by  Mr.  B.  F.  Floyd  of  the  Fla.  Exp.  Sta. 


368 


FUNGOUS  DISEASES  OF  PLANTS 


The  mycelia  of  both  the  blotch  and  the  speck  are  superficial,  at 
most  merely  roughening  the  surface  of  the  cuticle.    The  blotches 

are  irregular  in 
outline,  sometimes 
coalescing  into 
large  areas.  The 
specks,  as  the  name 
indicates,  are  small, 
circular,  dark  col- 
ored flecks  associ- 
ated in  groups,  and 
sometimes  distrib- 
uted over  large 
areas. 

A  network  of  ra- 
diating olive-brown 
or  fuliginous  hyphae 
made  up  of  more  or 
less  barrel-shaped 
cells  constitute  the 
blotch.  Cell  fusions  and  cell  aggregations  are  common.  On  the 
other  hand,  the  specks  are 
at  first  dense  aggregates 
of  rather  light  colored  hy- 
phae, and  from  such  specks 
delicate  hyphae  may  be 
traced  to  similar  neighbor- 
ing spots  or  to  blotches. 
A  mature  speck  becomes 
shining  black  and  dry. 
Then  the  central  portion 
breaks  away  and  is  pre- 
sumably the  source  of  new 
infections.  No  spore  form 
has  been  found  accom- 
panying this  phase.  Both 

£    r  i  FIG.  188.    LEPTOTHYRIUM  POM/:  DEVELOP- 

types   of    fungus    have,      MENT  QF  PYCNIDIA  FROM  PYCNOSCLEROTIA 

however,  been   followed  (Photograph  by  B.  F.  Floyd) 


FIG.  187.  FLY  SPECK  AND  SOOTY  BLOTCH  OF  APPLE 


FUNGI  IMPERFECTI  369 

throughout  the  autumn  and  winter  and  careful  sections  made  at 
different  times.  In  the  case  of  the  blotch,  as  the  season  advances, 
the  cell  aggregates  may  develop  a  definite  sclerotial-like  body 
(November  in  Missouri).  By  March  this  body  has  differentiated 
into  a  pycnidium  (Fig.  188)  25  to  ioo//,  in  diameter,  of  the 
Leptothyrium  type,  bearing  hyaline,  elliptical  spores.  The  latter 
measure  12-14  X  2-3  //,. 


CHAPTER   XIII 

HEMIBASIDIOMYCETES 

I.    USTILAGINALES 

BREFELD,  O.    Die  Brandpilze,   I.  Unters.  a.  d.  Gesammtgeb.  d.  Mykologie  5  : 

1-220.  pis.  1-13.    1883. 

BREFELD,  O.,    u.  FALCK,  R.    Ibid.  13 :   1-75.  pis.  1-2.    1905. 
CLINTON,  G.  P.    North  American  Ustilagineae.    Proc.  Boston  Soc.  Nat.  Hist. 

31:   329-529-    I9°5- 
DANGEARD,  P.  A.    Recherches  histologiques  sur  la  Famille  des  Ustilaginees. 

Le  Botaniste  3  :   240-281.    1892. 
DEBARY,  A.    Die  Brandpilze,    144  pp.    8  pis.    1853. 
DIETEL,   P.    Ustilagineae  und  Tilletiinese.    Natiirl.    Pflanzenfam.    (Engler  u. 

Prantl,  Red.)    1  (Abt.  i  *  *) :  2-24.  figs.  i-ij. 
FISCHER  DE  WALDHEIM,  A.    Beitrage  zur  Biologic  u.  Entwickelungsges.  d. 

Ustilagineen.    Jahrb.  f.  wiss.  Bot.  7:  61-144.  Pls-  7-12.    1870. 
HARPER,  R.  A.    Nuclear  Phenomena  in  Certain  Stages  in  the  Development 

of  the  Smuts.    Trans.  Wis.  Acad.  Sci.,  Arts,  and  Letters  12 :  475-498. 

pis.  8-9.    1899. 
PLOWRIGHT,  C.  B.    A  Monograph  of  the  British  Uredineae  and  Ustilagineae. 

347  pp.    8  pis.    1889. 
TULASNE,  L.  R.  et  C.    Me'moire  sur  les  Ustilaginees  comparers  aux  Uredi- 

ne'es.    Ann.  d.  Sci.  Nat.  (Bot.)  7  (3  Ser.):   12-127.    pk-  2-7.    1847. 

The  Ustilaginales,  commonly  known  as  the  "  smut  fungi,"  repre- 
sent, in  the  opinion  of  most  mycologists,  what  may  be  considered 
the  lowest  of  the  basidium  class.  Without  exception,  they  are 
parasitic  fungi,  and  they  occur  upon  herbaceous  flowering  plants. 
Many  species  infect  grasses.  There  are,  however,  thirty-five 
families  of  host  plants  in  North  America  alone,  representing 
(according  to  Clinton)  one  hundred  and  sixty-four  genera  and 
four  hundred  and  forty-two  species. 

The  method  of  infection  is  diverse.  In  a  few  species  infection 
is  apparently  limited  to  the  germinating  seedlings,  in  many  cases, 
however,  taking  place  through  any  meristematic  tissues.  The 
mycelium  may  extend  throughout  the  entire  plant  or  it  may  be 
located  in  limited  areas,  sometimes  being  confined  to  particular 
organs  of  the  plant.  It  is  commonly  intercellular,  frequently 
developing  haustoria.  Upon  the  production  of  spores  it  may 
disappear  by  a  gelatinization  process.  Reproduction  is  seldom  by 

370 


HEMIBASIDIOMYCETES  371 

means  of  conidia  produced  on  the  external  portion  of  the  host,  as 
in  Entyloma,  and  typically  by  means  of  chlamydospores  formed 
within  interstitial  or  terminal  cells  or  hyphae.  Chlamydospores  are 
for  the  most  part  dark  colored,  simple  or  agglutinated,  and  with  or 
without  sterile  appendage  cells.  The  chlamydospores  produce  upon 
germination  a  basidium-like  structure  known  as  a  promycelium, 
which  in  turn  originates  lateral  or  terminal  sporidia.  In  this  order 
the  fusion  of  sporidia,  or  of  germ  tubes  from  these,  is  common. 
This  cell  fusion  is  not  accompanied  by  nuclear  fusion.  Each 
sporidium  is  provided  with  a  single  nucleus. 

This  order  is  divided  into  two  families,  Ustilaginaceae  and 
Tilletiaceae,  based  upon  characters  which  become  evident  only  in 
germination.  The  characters  are  therefore  largely  those  of  the 
germ  tube  or  promycelium. 

Ustilaginaceae.  Spore  masses  are  made  up  of  simple  or  com- 
pound spores.  The  promycelium  is  usually  divided  into  two  or. 
four  cells,  originating  both  lateral  and  terminal  sporidia,  which 
sporidia,  in  saccharine  or  other  nutrient  solutions,  are  for  the  most 
part  able  to  bud  after  the  fashion  of  yeast  fungi  for  an  almost 
indefinite  period  of  time.  This  family  includes  from  seven  to 
eleven  genera,  according  to  different  authorities. 

The  characters  of  only  three  genera  need  to  be  considered  in 
order  to  become  familiar  with  the  basis  of  classification. 

1.  Spores  single,  spore  masses  dusty  at  maturity  and  without  any  sort  of 

inclosing  membrane Ustilago 

2.  Spores  agglutinated  in  balls,  spore  masses  more  or  less  dusty.    Spore 

balls  usually  evanescent,  spores  very  dark Sorosporium 

3.  Spores  agglutinated  in  balls,  spore  masses  more  or  less  dusty.    Spore 

balls  rather  permanent,  spores  now  adhering  by  folds  or  thickenings 
of  the  outer  coat Tolyposporium 

Tilletiaceae.  Spore  masses  are  made  up  of  simple  or  compound 
spores ;  these  masses  dusty  and  exposed,  or  imbedded  in  the  tis- 
sues. The  promycelium  is  short,  originating  usually  an  apical  clus- 
ter of  more  or  less  filiform  sporidia.  The  latter  may  fuse  in  pairs, 
and  whether  fusing  or  not,  may  produce  secondary  conidia,  or  may 
germinate  directly  into  infection  hyphae. 

This  family  includes  from  eight  to  ten  groups  of  generic  rank, 
the  differentiated  characters  of  three  of  which  may  be  indicated. 


372  FUNGOUS   DISEASES  OF  PLANTS 

1.  Spores  single,  spore  masses  dusty,  spores  without  conspicuous  tube-like 

hyaline  appendage Tilletia 

2.  Spores  single,    Spores  in  loose  groups,  imbedded  in  the  tissues.  Entyloma 

3.  Spores  agglutinating  in  balls,  spore  masses  dusty,  spore  balls  invested 

with  a  cortex  of  sterile  cells    .     .     .     ..    :.    ".'.".     .     Urocystis 


II.    LOOSE  SMUT  OF  OATS 
Ustilago  Avena  (Pers.)  Jens. 

JENSEN,  J.  L.    Om  Kornsorternes  Brand.    Copenhagen,  1888. 

KELLERMAN,  W.  A.,  and  SWINGLE,  W.  T.  Loose  Smut  of  Cereals.  Kansas 
Agl.  Exp.  Sta.  Kept.  2:  213-288.  pis.  1-9.  1890. 

KELLERMAN,  W.  A.,  and  SWINGLE,  W.  T.  Additional  Experiments  and  Ob- 
servations on  Oat  Smut.  Kan.  Agl.  Exp.  Sta.  Built.  15:  93-133-  l89°- 

STUART,  W.  Formalin  as  a  Preventive  of  Oat  Smut  Ind.  Agl.  Exp.  Sta. 
Built.  87:  1-26.  1901. 

SWINGLE,  W.  T.  The  Grain  Smuts.  U.  S.  Dept.  Agl.  Farmers'  Built.  75 : 
1-20.  figs.  1-8.  1898. 

The  loose  smut  of  oats  is  one  of  the  most  common  and  destruc- 
tive of  the  smut  family.    It  is  found  wherever  oats  are  cultivated, 

and  it  would  not  appear  that 
climatic  conditions  influence 
materially  the  abundance  of 
the  fungus.  Besides  the  vari- 
ous varieties  of  the  cultivated 
oats  (Avena  sativa),  it  has  only 
been  reported  upon  Avena 
fatua,  the  latter  in  California. 
Like  most  of  the  other 
loose  smuts  of  grain,  it  ma- 
tures at  or  about  the  time  the 
grain  is  in  flower,  and  dur- 
ing the  ripening  season  it  is 
widely  distributed.  The  gen- 
eral appearance  of  the  loose 
smut  is  striking,  and  usually 
as  shown  in  Fig.  189.  It  has 
been  estimated  that  the  aver- 
age loss  to  the  oat  crop 
throughout  this  country  may 
FIG.  189.  LOOSE  SMUT  OF  OATS  be  placed  at  about  eight 


HEMIBASIDIOMYCETES  373 

per  cent.  This  estimate  would  mean  a  loss  of  about  twenty  million 
dollars,  based  upon  the  statistics  of  oats  produced  during  1906. 

The  mycelium  of  the  oat  smut  is  present  throughout  the  tissues 
of  the  affected  plants.  Infection  takes  place  by  means  of  the  germi- 
nating conidia  at  the  time  of  germination  of  the  seed.  The  mycelium 
branches  abundantly  in  practically  all  tissues  of  the  developing 
flowers,  completely  infesting  the  young  ovule  and  the  inclosing 
floral  structures.  The  mycelium,  at  the  time  that  spore  formation 
becomes  evident,  shows  a  nodulate  appearance,  and  the  branches 
are  closely  fascicled,  like  clusters  of  grapes.  Within  each  swollen 
area  of  the  mycelium  a  chlamydospore  is  found.  As  the  chlamydo- 
spores  mature,  the  inclosing  walls  of  the  parent  hyphae  and  much 
of  the  general  mycelium  which  is  not  differentiated  into  spores 
gelatinizes  or  otherwise  breaks  away,  and  the  spores  are  set  free 
in  large  masses.  With  the  increased  growth  of  the  mycelium  and 
the  formation  of  spores,  the  softer  cells  of  the  host  plant  are  rapidly 
absorbed,  so  that  at  maturity  only  the  more  resistant  tissues  of  the 
florets  may  remain,  the  whole  ovule  with  its  inclosing  glumes  being 
largely  converted  into  the  dusty  mass  of  sooty  spores.  In  a  closely 
related  species  of  oat  smut  (Ustilago  levis),  long  regarded  merely 
as  a  race  or  variety  of  Ustilago  Avence,  the  mycelium  destroys  only 
the  kernels  and  does  not  attack  the  glumes.  The  smut  therefore 
remains  inclosed  or  hidden. 

The  spores  are  almost  spherical  or  slightly  ovoidal,  and  echinu- 
late,  varying  in  length  from  5  to  9  ft.  They  are  also  olivaceous 
in  color,  with  a  lighter  area  at  one  side.  Germination  of  the  fresh 
or  of  preserved  spores  may  be  readily  secured.  In  fact,  in  herbarium 
material  spores  may  preserve  their  vitality  for  several  years.  Ger- 
mination may  proceed  in  pure  water  or  in  nutrient  solution. 

The  promycelium  is  frequently  four-celled,  though  somewhat 
variable  in  this  regard,  and  it  often  assumes  abnormal  forms,  as 
shown  in  Fig.  190.  The  conidia  are  produced  laterally  and  termi- 
nally. They  are  elliptical  or  subelliptical  in  form  and  measure 
4.5-8x4.5-6;*.  In  nutrient  solutions  the  well-known  budding 
of  the  conidia  may  continue  almost  indefinitely,  and  under  certain 
conditions,  or  after  extensive  cultivation,  mycelium-like  cells  may  be 
produced.  Upon  the  living  host,  however,  the  conidia  germinate 
by  the  production  of  an  infection  hypha. 


374 


FUNGOUS  DISEASES  OF  PLANTS 


Control.  In  an  endeavor  to  control  smut  in  oats,  bunt  in  wheat, 
and  other  more  or  less  similar  diseases,  a  careful  study  has  been 
made  of  a  variety  of  fungicides  or  toxic  agents  in  solution,  and  of 
hot  water. 

The  hot  water  treatment  of  the  seed  grain  is  the  method  in 
more  common  use.  This  method  consists  in  immersing  for  ten 
minutes  in  water  at  a  temperature  of  from  132°  to  133°  F.  It  has 
been  found  desirable  to  put  the  seeds  into  a  basket  or  perforated 
tin  vessel,  and  this  may  be  previously  dipped  into  warm  water  at  a 
temperature  of  about  110°  to  120°  F.,  in  order  that  the  tempera- 
ture of  the  hot  water  may  not  be  greatly  reduced  by  using  cold 
seed.  The  water  in  which  the  seeds  are  finally  immersed  should 

be  retained  during 
the  ten  minutes  at 
a  temperature  of 
not  less  than  130°, 
otherwise  additional 
warm  water  should 
be  added  during  the 
process.  Further- 
more, it  is  desirable 
to  throw  the  seed 
into  cold  water  be- 
fore treatment,  so 
that  the  smutted 


FIG.  190.    USTILAGO  AVENGE:  GERMINATING  SPORES 


seed  may  be  floated  and  skimmed  off,  for  the  treatment  would  be 
of  small  value  if  the  large  quantity  of  spores  still  held  within  the 
kernels  of  smutted  grain  were  not  removed.  The  hot  water  method 
is  effective,  but  since  it  appears  somewhat  complicated,  it  is  now 
being  superseded  by  a  formalin  treatment.  In  its  simplest  terms 
the  latter  consists  in  dipping  the  seed  in  a  solution  containing 
i  pint  of  formalin  to  30  gallons  of  water.  The  seed  may  be  put 
into  sacks  or  baskets  of  from  \  to  i  bushel  each,  and,  as  before, 
immersed  in  the  barrel  of  formalin  solution  for  about  ten  minutes, 
drained,  put  away  wet  in  the  sacks,  or  heaped  and  covered  for  two 
hours  and  finally  spread  out  to  dry  rapidly  before  danger  of  germi- 
nation. Shoveling  over  will  facilitate  the  drying.  Copper  sulfate, 
potassium  sulfide,  and  other  germicides  have  also  been  employed. 


HEMIBASIDIOMYCETES  375 

III.    LOOSE  SMUT  OF  WHEAT 
Ustilago  Tritid  (Pers.)  Jens. 

BREFELD,  O.,  u.  FALK,  R.     Unters.  13 :   /.  c.  (Die  Bluteninfektion  bei  den 

Brandpilzen). 
FREEMAN,  E.  M.,  and  JOHNSON,  E.  C.    The  Loose  Smuts  of  Barley  and 

Wheat.    Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  152:    1-43.    pis.  1-6. 

1909. 
SWINGLE,  W.  T.    The  Grain  Smuts,  /.  c.  (see  Ustilago  Avencz). 

The  above  species,  producing  the  well-known  loose  smut  of 
wheat,  is  almost  as  widely  distributed  as  the  organism  producing 
the  loose  smut  of  oats.  The  general  appearance  of  the  affected 
plant  at  the  time  of  flowering  is  much  the  same  as  in  the  case  of 
oats,  and  in  many  respects  the  life  histories  of  the  two  species  are 
similar.  This  species  is  found  upon  practically  all  varieties  of  wheat 
and  under  all  climatic  conditions.  Morphologically,  this  fungus  is 
scarcely  to  be  distinguished  from  the  oats  smut,  and  this  is  true 
whether  one  considers  the  form  of  the  spores  or  the  characters 
made  evident  upon  germination  ;  but  the  absolute  failure  of  cross 
inoculations  indicates  that  the  two  forms  are  distinct.  According 
to  recent  investigations,  moreover,  it  would  appear  that  this  species 
may  also  gain  entrance  to  the  host  plant  at  the  time  of  flowering.  It 
is  stated  that  the  infection  tube  penetrates  the  stigma  and  style,  and 
by  that  means  enters  the  developing  seed.  In  the  developing  seed 
it  retains  its  vitality  and  grows  up  through  the  plant  when  the  seed 
germinates.  This  mode  of  infection  is  said  to  be  the  most  com- 
mon ;  therefore,  according  to  these  results,  treatment  of  the  seed 
wheat  for  loose  smut  might  seem  to  be  useless  ;  nevertheless,  from 
experiments  which  have  been  made  in  this  country,  it  would  seem 
that  a  modified  method  of  Jensen's  hot  water  treatment  is  partially 
effective  against  this  fungus.  It  appears  at  present  possible  to  assign 
a  cause  for  this  latter  fact.  It  does  not  seem  to  be  due  to  a  greater 
number  of  infections  through  seedling  stages  than  is  now  assumed, 
and  is  presumably  due  to  the  killing  of  the  fungus  within  the  tissues 
by  the  hot  water  method. 

Control.  In  view  of  the  recent  studies  upon  blossom  infection, 
it  would  seem  that  the  only  reliable  means  of  prevention  would 
consist  in  the  hot  water  treatment  together  with  seed  selection. 
It  would  be  necessary  to  select  seed  from  a  field  free  of  smut. 


376 


FUNGOUS  DISEASES  OF  PLANTS 


Where  the  disease  is  very  abundant  it  would  be  practicable,  on 
plats  to  be  employed  for  seed,  to  weed  out  smutted  plants  prior  to 
final  maturity.  The  most  recent  recommendation  with  respect  to 
seed  treatment  is  to  soak  five  hours  in  cold  water,  and  then  ten 
minutes  in  water  at  54°  C. 


IV.    SMUT  OF  CORN 
Ustilago  Zece  (Beckm.)  Ung. 

ARTHUR,  J.  C.,  and  STUART,  W.   Corn  Smut.    Ind.  Agl.  Exp.  Sta.  Ann.  Kept. 

12:  84-135.    1900. 
HITCHCOCK,  A.  S.,  and  NORTON,  J.  B.  S.   Corn  Smut.    Kan.  Agl.  Exp.  Sta. 

Built.  62:   169-212.  pis.  i -10.    1896. 
KNOWLES,  E.  L.    A  Study  of  the  Abnormal  Structures  Induced  by  Ustilago 

Zeas-mays.    Journ.  Myc.    5:   14-18.  pis.  2-7.    1889. 

The  common  smut  of  corn  (Zea  mays] 
occurs  in  all  regions  where  maize  is  grown. 
It  is  productive  of  considerable  losses  at 
times,  and  it  is  probable  that  in  many  corn- 
growing  sections  the  yearly  loss  will  aver- 
age as  high  as  5  per  cent.  It  may  vary, 
however,  from  o  to  about  25  per  cent. 

Habitat  relations.  This  fungus  some- 
times causes  enormous  enlargements  of 
various  parts  of  the  host,  occurring  in 
staminate  and  pistillate  flowers,  on  the 
stalk,  especially  at  the  nodes,  and  also  in 
the  leaves.  The  abnormalities  or  swellings 
are  usually  prominent  and  often  attain  the 
size  of  several  inches  in  diameter.  Very 
careful  experiments  throughout  a  long 
period  of  time  have  made  it  clear  that 
infection  takes  place  through  any  young 
and  growing  tissue,  but  that  the  plant  is 
not  affected,  as  a  rule,  until  a  foot  or 
more  in  height.  The  spores  retain  their 
vitality  in  the  soil  for  some  time,  and  the 
sporidia  may,  by  a  sprouting  process,  be  propagated  and  dissem- 
inated through  manure  or  compost  spread  upon  the  land.  The 


FIG.  191.    USTILAGO 
SMUT  OF  CORN 


HEMIBASIDIOMYCETES 


377 


mycelium  is  rather  sparsely  distributed  throughout  the  general  area 
of  normal  tissue,  from  which  swellings  arise,  but  it  becomes  devel- 
oped at  certain  points  in  quantity  in  the  form  of  pockets,  in  which 
areas  it  is  later  differentiated  into  the  spores.  Upon  the  stem  the 
abnormal  growth  has  been 
found  to  originate  principally 
just  beneath  the  epidermis, 
that  is,  outside  of  the  area 
of  the  fibrovascular  bundles. 
Rapid  multiplication  of  the 
host  cells  occurs,  and  these 
become  diverse  and  always 
abnormal  in  form.  Neighbor- 
ing bundles  send  branches 
into  the  abnormal  tissue,  and" 
the  bundles  at  some  little  dis- 
tance may  also  show  consider- 
able variation  from  the  normal 
type.  At  maturity  cells  of  the 
host  are  very  largely  broken 
down,  and  the  pockets  of 
spores  are  surrounded  by  a 
membrane  made  up  of  modi- 
fied fungous  threads  mingled 
together  with  dried  host  cells. 
This  membrane  is  soon  broken 
and  the  loose  spores  are  set 

free.  The  spores  are  more  or  less  spherical,  though  sometimes 
irregular,  measuring  often  8-i2/>t,  and  the  walls  are  beset  with 
blurit  echinulations.  The  spores  germinate  readily  in  water  or  in 
nutrient  solutions  in  the  normal  manner.  This  fungus  is  known 
only  upon  one  host  besides  the  corn,  that  is,  Etichlcena  luxurians. 
One  other  species  of  smut  is  found  upon  the  corn,  Ustilago 
Reiliana,  but  this  is  readily  distinguished  from  the  common  smut. 
Control.  Since  this  fungus  may  gain  entrance  to  the  host  at 
any  time,  prevention  consists  in  cutting  out  the  affected  stalks 
before  the  spores  mature.  Such  stalks,  moreover,  should  be 
destroyed  and  not  thrown  upon  the  compost  heap  where  the 


FIG.  192.    USTILAGO  NUDA:  LOOSE  SMUT 
OF  BARLEY 


378  FUNGOUS  DISEASES  OF  PLANTS 

fungus  will  multiply  itself  and  be  returned  to  the  land  in  a  form 
to  do  considerable  damage  to  the  crop  the  following  season.  It  is 
commonly  stated  that  fields  heavily  fertilized  with  barnyard  manure 
develop  a  higher  percentage  of  smutted  corn. 


V.    SMUT  OF  BLUE-STEM  GRASS 
Sorosporium  Syntherismce.  (Pk.)  Farl. 

For  the  most  part,  the  various  species  of  Sorosporium  occur 
upon  the  so-called  blue-stem  and  poverty  grasses,  belonging  to  the 
genus  Andropogon  and  Aristida.  Several  species  are  therefore 
common  but  of  slight  economic  importance.  Sorosporium  Synthe- 
rismce is  found,  however,  upon  several  species  of  Panicum  and 
Cenchrus,  and  is  quite  widely  distributed  throughout  the  United 
States.  The  sori  are  usually  confined  to  the  inflorescence,  the 
whole  of  which  may  or  may  not  be  affected.  At  maturity  they  are 
inclosed  in  a  false  membrane,  somewhat  similar  to  that  in  Ustilago 
Zece,  which  ruptures,  exposing  the  spore  masses  and  shred-like 
remnants  of  host  tissue.  The  spores  adhere  together  in  spore  balls 
for  a  relatively  short  time,  the  balls  being  usually  variable  in  shape, 
measuring  from  50  to  100/1,  in  length.  The  spores  are  spheroidal 
or  irregular  in  outline,  measuring  9  to  1 3  /-t,  and  they  are  covered 
with  minute  wart-like  projections. 

VI.    TOLYPOSPORIUM  BULLATUM  (Schroet.)  Schroet. 

The  above  species  is  probably  the  most  widely  distributed  of 
this  genus  in  the  United  States.  It  occurs  upon  the  common  barn- 
yard grass  (Echinochloa  crusgalli).  The  sori  are  confined  to  the 
ovule  sacs,  and,  as  in  the  preceding  species,  they  are  covered  wjth 
a  membrane  which  upon  being  ruptured  exposes  the  spore  balls. 
The  latter  are  from  50  to  1 60  /t  in  length,  black  and  opaque,  con- 
sisting of  one  hundred  or  more  closely  united  spores.  The  spores 
appear  flavous  or  reddish  brown.  According  to  Clinton  they  are 
11  covered  with  a  thin,  tinted,  outer  coat,  more  or  less  folded  in 
ridges,  by  which  the  spores  are  bound  together,  and  which,  on  the 
rupturing  of  the  spore  balls,  often  show  as  spiny  projections  at  the 
spore  margins,  usually  ovoidal,  spherical,  or  polyhedral,  7  to  12  /A." 


HEMIBASIDIOMYCETES  379 

VII.    BUNT,  OR  STINKING  SMUT  OF  WHEAT 
TiUetia  fattens  (B.  &  C.)  Trel. 

KELLERMAN,  W.  A.,  and  SWINGLE,  W.  T.  Preliminary  Experiments  with 
Fungicides  for  Stinking  Smut  of  Wheat.  Kan.  Agl.  Exp.  Sta.  Built.  12  : 
27-50.  pi.  i.  1890. 

KELLERMAN,  W.  A.  Second  Report  on  Fungicides  for  Stinking  Smut  of 
Wheat.  Kan.  Agl.  Exp.  Sta.  Built.  21:  47-72.  1891. 

Distribution  and  symptoms.  The  above  species  is  the  more 
commonly  distributed  smut  of  this  family  upon  grain  in  the  United 
States,  and  while  very  commonly  found  in  greater  or  less  abun- 
dance, it  is  nevertheless  entirely  absent  from  some  considerable 
wheat-growing  regions.  On  the  other  hand,  in  portions  of  the 
Northwest,  and  extending  also  into  Canada,  there  are  regions  in 
which  the  losses  from  this  fungus  have  amounted  to  from  one  half 
to  two  thirds  of  a  crop.  The  fungus  affects  the  various  varieties  of 
wheat,  but  is  not  found  upon  any  other  grain.  Little  definite  infor- 
mation, however,  has  accumulated  concerning  the  susceptibility  of 
different  varieties  to  attack.  The  abundance  of  disease  in  certain 
regions  would  not  seem  to  be  greatly  influenced  by  climatic  con- 
ditions, but  is  probably  very  largely  due  to  unfortunate  practices  in 
seed  selection  and  to  continuous  cropping  with  wheat.  The  pro- 
duction of  spores  in  the  tissues  of  the  host  is  confined  very  largely 
to  the  ovule  sacs,  at  maturity  the  kernels  being  the  chief  seat  of  the 
spore  masses.  The  spores  are  permanently  concealed  by  the  glumes 
which  envelop  the  kernels ;  but  smutted  heads  are  more  or  less 
recognizable  on  account  of  a  slight  difference  in  color  and  a  some- 
what emphasized  flaring  habit  of  the  spikes,  due  perhaps  to  slightly 
larger  size  of  the  infected  kernels.  The  spores  give  rise  to  a  pene- 
trating and  disagreeable  odor,  which  becomes  very  evident  in  the 
bin -or  during  the  milling  process.  In  general,  all  of  the  kernels  of 
a  spike  will  be  infested. 

The  fungus.  The  spores  are  brown  in  color,  usually  oblong  to 
spherical  in  form,  with  a  smooth  wall,  varying  considerably  in  size, 
extremes  being  more  than  from  1 6  to  25  /x  in  length.  The  germi- 
nation of  the  spores  of  this  species  conforms  well  to  the  description 
given  for  the  whole  family.  The  acicular  or  needle-shaped  sporidia, 
which  are  produced  in  the  form  of  a  crown  on  a  short,  continuous 
promycelium,  frequently  unite  in  pairs,  and  secondary  sporidia 


380  FUNGOUS  DISEASES  OF  PLANTS 

may  be  produced.  Infection  takes  place  through  the  young  wheat 
seedling,  and  the  spores  are  very  generally  distributed  by  means 
of  the  seed. 

Control.  Bunt  of  wheat  has  very  generally  been  successfully 
treated  by  the  methods  recommended  for  oat  smut.  The  formalin 
treatment  is  preferred.  In  applying  this  method,  however,  some 
prefer  to  sprinkle  the  wheat  with  the  formalin  solution  (i  pint  to 
30  gallons)  rather  than  to  soak  the  seed. 

VIII.    TILLETIA:    OTHER  SPECIES 

Tilletia  Tritici  (Beij.)  Wint.  This  species  also  occurs  upon  the 
wheat  and  was  long  considered  to  be  merely  a  spiny  or  reticulately 
marked  form  of  Tilletia  fastens.  Experiments  have  demonstrated 
that  the  fungi  are  distinct.  This  species  is  less  frequently  found, 
but  when  present  it  produces  practically  the  same  effects  as  those 
described  for  the  fungus  last  discussed.  It  sometimes  occurs  in 
conjunction  with  Tilletia  fee  tens.  A  microscopic  examination  per- 
mits an  easy  identification,  since  the  reticulations  on  the  wall  of  the 
spore  are  marked  in  this  species.  The  spores  are  very  nearly  equal 
in  size  to  those  of  the  preceding  and  measure  16—22  /*  in  diameter. 

Tilletia  horrida  Tak.  This  fungus  occurs  in  the  ovaries  of  the 
cultivated  rice,  and  it  is  now  widely  distributed  in  the  United  States 
as  well  as  in  the  Orient.  It  is  concealed  by  the  enveloping  blossoms 
and  is  not  readily  observed  in  the  field.  The  spores  are  subspherical, 
measuring  22-33/4  in  length.  A  band  of  scales  2-4/1  in  width, 
due  to  the  thickenings  in  the  outer  hyaline  wall,  is  generally  evident. 

Tilletia  corona  Scrib.  This  species  occurs  upon  plants  related 
to  the  rice,  namely,  members  of  the  genus  Leersia,  and  it  is 
common  upon  these  plants  in  their  natural  habitats  in  the  south- 
ern states. 

IX.    ENTYLOMA 

Entyloma  Physalidis  (Kalchb.  &  Cke.)  Wint.  The  smut  fungi 
of  the  genus  Entyloma  are  not  commonly  productive  of  conspicu- 
ous deformities.  In  the  case  of  Entyloma  Physalidis  pale  spots 
are  produced  upon  the  leaf  of  the  ground  cherry,  or  love-apple 
(Physalis  pubescens}.  The  spores  are  intermediate  in  size,  10-16/11 
in  length,  and  they  are  situated  in  small  masses,  or  beds,  scattered 


HEMIBASIDIOMYCETES  38 1 

throughout  the  affected  areas.  They  are  light  in  color,  often  nearly 
hyaline.  The  distribution  of  the  spores  is  only  effected  by  disinte- 
gration of  the  leaf.  There  are,  however,  conidia  in  the  life  history 
of  some  species  of  this  genus  of  smuts.  In  this  species  they  are 
scolecosporic  in  form,  30-55  x  1-2  p.  No  very  serious  diseases 
of  cultivated  plants  are  induced  by  species  of  Entyloma,  although 
the  genus  is  rich  in  forms. 

Entyloma  compositarum  Farl.  is  widespread  in  the  United  States 
upon  a  variety  of  the  composites,  including  among  these  species 
of  Ambrosia,  Aster,  Erigeron,  etc.  The  minute  sori  occur  in  the 
leaves.  The  spores  are  subspherical  or  ovoidal,  9-14/4,  and  hyaline. 
The  under  surfaces  of  the  leaves  may  be  profusely  covered  with 
the  conidial  form,  which  is  in  this  case  like  a  species  of  Cercospo- 
rella  with  relatively  short  spores  and  conidiophores.  The  conidia 
are  fusiform  or  slightly  clavate  and  measure  1 5-20  x  2-3  p. 

Entyloma  Ranunculi  (Bon.)  Schrot.1  is  found  upon  various 
species  of  Ranunculaceae.  The  life  history  of  this  form  has  been 
carefully  studied. 

X.    ONION  SMUT 
Urocystis  Cepulce.  Frost 

SELBY,  A.  D.    Onion  Smut.    Ohio  Agl.  Exp.  Sta.  Built.  122:  71-84.   figs. 

3,4.    1900. 
SIRRINE,   F.  A.,  and   STEWART,  F.  C.    Experiments  on  the  Sulphur-Lime 

Treatment  for  Onion  Smut.    N.  Y.  Agl.  Exp.  Sta.  Built.  182:   145-172. 

1900. 
STURGIS,  W.  C.    Transplanting,  as  a  Preventive  of  Smut  upon  Onions.  Conn. 

Agl.  Exp.  Sta.  Kept.  19 :   176-182.    1895. 
THAXTER,  ROLAND.  The  "  Smut "  of  Onions  (Urocystis  Cepulce).   Conn.  Agl. 

Exp.  Sta.  Kept.  (1889):  129-153.  pis.  1-2. 

Habitat  relations.  The  onion  smut  has  been  known  as  an 
important  disease-producing  organism  in  the  United  States  for 
about  forty  years,  the  first  published  notes  of  its  effects  being 
in  the  reports  of  the  Massachusetts  State  Board  of  Agriculture, 
1869  to  1870.  The  fungus  seems  to  be  of  American  origin  and 
its  injuries  are  very  largely  confined  to  the  eastern  states,  particu- 
larly New  England.  It  occurs,  however,  as  far  west  as  Indiana. 
It  would  not  appear  that  climatic  conditions  affect  the  prevalence 

1  Ward,  H.  M.    On  the  Structure  and  Life  History  of  Entyloma  Ranunculi 
-(Bon.).    Phil.  Trans.  Royal  Soc.  London.    178  B:  173-185.  pis.  3,  4.    1887. 


382 


FUNGOUS  DISEASES  OF  PLANTS 


of  the  organism,  nor  does  it  seem  that  soil  conditions  are  of  any 
great  importance.  The  host  frequently  shows  the  presence  of  the 
fungus  soon  after  the  first  leaf  appears.  Dark  spots  are  usually 
first  noticed  just  below  the  knee  of  the  first  leaf,  and  these  are 
frequently  repeated  in  the  leaves  subsequently  formed.  The 
whole  plant  may  therefore  be  very  largely  infected,  although  in 

exceptional  cases 
the  fungous  my- 
celium seems  to 
have  directed  it- 
self into  the  first 
leaf  and  disap- 
peared upon  the 
withering  of  this 
organ.  Soon 
after  the  spots 
are  noticed  upon 
the  leaves  longi- 
tudinal rifts  are 
formed,  and 
there  are  ex- 
posed threads 
of  fibrous  tissue, 
together  with 
quantities  of  a 
granular  spore 
powder,  which 
latter  consists  of 
the  characteristic 
spore  masses  or 
balls.  Fig.  193,^ 
shows  an  onion 
with  a  character- 
istic form  of  disease.  The  spore  balls  are  washed  into  the  soil, 
if  diseased  bulbs  are  not  promptly  removed,  and  the  soil  is  un- 
questionably the  chief  source  of  the  annual  infection.  It  is 
possible  that  the  spores  may  also  adhere  to  the  surfaces  of 
the  seed  and  thus  further  disseminate  the  fungus. 


FIG.  193.    UROCYSTIS,  GENERAL  CHARACTERISTICS 
(a,  b,  and  c,  after  Thaxter) 

a,  6,  and  c,  Urocystis  Cepula ;  rf,  Urocystis  occulta 


HEMIBASIDIOMYCETES  383 

The  fungus.  It  has  been  ascertained,  apparently  beyond  doubt, 
that  the  spores  may  often  retain  their  capacity  for  germination 
in  the  soil  for  a  period  of  twelve  years.'  The  spore  balls  are  more 
or  less  spherical  in  general  outline  and  vary  from  17  to  2  5  ^  in 
greatest  diameter.  The  spores  in  a  ball  may  number  several,  but 
frequently  only  one  is  present.  The  sterile  cells,  which  usually 
form  a  complete  envelope,  are  slightly  colored,  generally  sub- 
spherical  in  form,  -4-8  /LI  in  length.  The  germination,  which  has 
been  carefully  figured,  commonly  conforms  to  that  of  this  family 
of  fungi  (Fig.  193,  b). 

Control.  Since  infected  soil  is  the  chief  source  of  trouble, 
it  is  practically  useless  to  treat  the  seed.  The  most  effective 
method  of  prevention  is  that  of  transplanting  the  seedlings,  the 
seed  having  been  previously  sown  in  a  bed  of  soil  known  to  be 
free  of  smut.  Since,  however,  transplanting  is  a  laborious  and 
expensive  process,  it  is  frequently  desirable  to  treat  the  land 
or  the  drill  in  which  the  seed  are  sown,  with  sulfur,  lime,  or 
formalin.  The  fungicides  mentioned  have  been  used  in  the  fol- 
lowing manner :  sulfur  and  air-slaked  lime  in  the  drill  at  the  rate 
of  100  pounds  of  sulfur  and  50  pounds  of  lime,  or  a  solution  of 
formalin  containing  I  pound  of  the  latter  to  30  gallons  of  water. 

Urocystis  occult  a  (Wallr.)  Reb.  on  rye  (Sec  ale  cere 'ale] ,  is  an- 
other species  of  this  genus  of  special  economic  importance  in  the 
eastern  and  north  central  states. 


CHAPTER  XIV 

PROTOBASIDIOMYCETES 
I.    RUST    FUNGI 

Uredinales 

ARTHUR,  J.  C.    Uredinales.    North  Amer.  Flora  7 :  85-160.    1907. 
ARTHUR,  J.  C.    Cultures  of  Uredineae;  in  1899,  Bot.  Gaz.  1900;  in  1900  and 

1901,  Journ.  Myc.  8  :  1902  ;  in  1902,  Bot.  Gaz.  35  :  1903  ;  in  1904,  Journ. 

Myc.  11  :    1905  ;  in  1905,  Journ.  Myc.  12:    1906. 
BLACKMAN,   V.    H.    On  the   Fertilization,  Alternation  of   Generations,   and 

General  Cytology  of  the  Uredineae.    Ann.  Bot.  18:  323-373.  ph.  21-24. 

1904. 
CHRISTMAN,  A.  H.    Alternation  of  Generations  and  the  Morphology  of  the 

Sporeforms  in  the  Rusts.    Bot.  Gaz.  44:  81-101.  pi.  7.    1907. 
ERIKSSON,  J.,  und  HENNING,  E.    Die  Getreideroste,  ihre  Geschichte  u.  Natur, 

sowie  Massregeln  gegen  dieselben.    463  pp.    ij  pis.    1896.    Stockholm. 
FISCHER,  E.    Die  Uredineen  der  Schweiz.    590  pp.  34.2  figs.    1904.    Bern. 
KLEBAHN,  H.    Die  Wirtswechselden  Rostpilze.    447  pp.    1894.   (Extensive 

bibliography,  which  see,  especially  for  important  papers  by  Klebahn  and 

others.) 
MCALPINE,  D.  The  Rusts  of  Australia.  Dept.  Agl.  Victoria.  349  pp.  55  pis. 

1 906.    (Also  extensive  bibliography.) 
OLIVE,  E.  W.    Sexual  Cell  Fusions  and  Vegetative  Nuclear  Divisions  in  the 

Rusts.    Ann.  Bot.  22:  331-360.  pi.  22.    1908. 
PLOWRIGHT,  C.  B.    A  Monograph  of  the  British  Uredineae  and  Ustilagineae, 

with  an  Account  of  their  Biology,  etc.    347  pp.    8  pis.    1889. 
RICHARDS,  H.  M.    On  Some  Points  in  the  Development  of  ^cidia.    Proc. 

Amer.  Acad.  Arts  and  Sci.  31 :   255-270.  pi.  i.    1895. 
SYDOW,  P.    Monographia  Uredinearum.    i.  Puccinia.   972pp.   1904.  Leipzig. 

The  Uredinales  comprise  about  two  thousand  species,  all  of 
which  are  obligate  parasites,  and  they  represent  perhaps  the  ex- 
treme of  obligate  parasitism.  In  no  case  has  it  been  possible  to 
grow  these  organisms  upon  artificial  media  or  apart  from  the 
hosts  beyond  the  stage  of  mere  germination  or  of  promycelial 
production.  The  host  plants  are  predominantly  the  Spermatophyta, 
or  seed  plants,  although  a  small  number  of  these  fungi  are  para- 
sitic upon  ferns.  The  host  deformities  vary  in  external  appear- 
ance from  almost  inconspicuous  discolorations  to  hypertrophies  of 
considerable  size,  on  the  one  hand,  or  to  extensive  witches'  brooms 

384 


PROTOBASIDIOMYCETES  385 

on  the  other.  The  production  of  spores,  particularly  the  produc- 
tion of  uredospores,  is  frequently  in  the  nature  of  rust-like  masses 
from  which  has  been  derived  the  common  name  applied  to  this 
family.  Popularly  the  term  rust  has  also  been  applied  to  certain 
leaf  spot  fungi,  but  this  usage  is  ill  advised. 

This  order  appears  to  be  somewhat  closely  related  to  the  smuts ; 
the  presence  of  a  promycelium  (promycelial-like  structure  in  the 
latter)  giving,  of  course,  the  chief  clue  to  this  relationship.  On 
the  other  liand,  however,  neglecting  the  feature  of  parasitism, 
there  is  a  close  relationship  with  the  saprophytic  Auriculariales, 
especially  if  we  regard  the  teleutospore  (promycelium,  etc.)  of  the 
rusts  as  the  all-essential  spore  form. 

The  mycelium  is  generally  local.  In  special  cases,  however,  it 
may  penetrate  through  a  considerable  extent  of  the  host,  and  it  is 
also  occasionally  perennial.  It  is  almost  invariably  intercellular, 
abundantly  branched,  rather  closely  septate,  and  provided  with 
haustoria.  The  effect  of  the  mycelium  upon  the  host  is  not  to  kill 
directly.  In  fact,  the  mycelium  may  develop  within  a  tissue  to  an 
enormous  extent,  yet  the  cells  of  the  invaded  tissue  may  remain 
completely  functional ;  and  death  may  result  only  when,  after 
abundant  fruiting  of  the  fungus,  the  rupture  of  the  epidermis  is 
considerable,  and  doubtless  the  withdrawal  of  nutrients  excessive. 
The  spores  which  may  be  produced  are  of  five  general  types,  as 
given  below. 

Spore  forms,  (i)  Spermatia  (or  pycnospores),  in  spermogonia 
(or  pycnidia) ;  (2)  aecidiospores,  in  cup-like  organs,  aecidia ;  (3) 
uredospores,  in  pustules  or  sori ;  (4)  teleutospores,  in  sori  simi- 
lar to  the  last ;  (5)  sporidia,  upon  a  promycelium  developed 
directly  from  the  teleutospore. 

A  species  may  include  from  one  to  five  (all)  of  these  types. 
The  relations  of  these  types  one  to  another  is  definite  and  the 
number  is  ordinarily  constant  in  the  species. 

The  spermatia  are  minute  spores  produced  in  flask-shaped 
conceptacles  (spermogonia  or  pycnidia).  They  are  supposed  to  be 
now  generally  functionless.  Many  mycologists  assume  that  they 
had  originally  the  function  of  one  sexual  gamete.  The  spermo- 
gonia are  commonly  associated  more  or  less  closely  with  the 
aecidia,  although  they  may  be  associated  with  other  spore  types. 


386  FUNGOUS  DISEASES  OF  PLANTS 

The  cecidia  are  essentially  cup-shaped  bodies  produced  by  the 
differentiation  of  a  compact  mass  of  hyphae  growing  perpendicular 
to  the  surface  of  the  host.  The  outer  layer  of  this  body  generally 
becomes  a  wall  or  peridium,  the  inner  hyphae  originating  each,  or 
each  pair,  a  chain  of  one-celled  spores  separating  at  maturity.  At 
first  sterile  cells  alternate  with  the  spore  cells,  but  these  practi- 
cally disappear  by  the  time  the  spores  are  mature.  Infection  by 
the  aecidiospore  commonly  results  in  the  production  of  uredo- 
spores,  less  frequently  teleutospores,  and  in  very  few  instances 
(so  far  as  can  be  ascertained)  another  generation  of  aecidiospores. 
The  peridium  is  variable,  and  four  types  corresponding  to  four 
form  gen-era  may  be  recognized :  in  some  cases  a  peridium  is  (i) 
absent  (Caeoma) ;  when  present  it  is  (2)  toothed,  the  body  being 
truly  cup-shaped  (yEcidium),  (3)  fimbriate,  the  body  being  elongate 
(Rcestelia),  or  (4)  irregularly  split  and  broken  (Peridermium). 

The  uredospores,  produced  ordinarily  in  masses  or  cushions 
(the  sori),  are  hyaline,  or  generally  yellow  to  dark  brown,  ovoidal 
or  spheroidal  spores  borne  generally  upon  pedicels,  which  are, 
however,  usually  deciduous.  In  a  few  genera  the  uredospores  are 
produced  in  chains.  The  walls  of  these  spores  are  frequently 
echinulate  or  warty,  and  there  are  from  two  to  ten  germ  pores 
meridionally  disposed.  Germination  may  proceed  immediately. 
The  germ  tube  penetrates  the  host  plant  through  the  stomata,  in 
general,  and  the  uredosporic  form  may  ordinarily  produce  re- 
peated generations  of  uredospores,  under  favorable  conditions. 
Later  in  the  season,  or  sometimes  under  less  favorable  conditions 
for  propagative  reproduction,  teleutospores  are  developed. 

Teleutospores  are  ordinarily  produced  in  sori  more  or  less 
similar  to  the  uredospores.  The  teleutospores  are  generally  thick- 
walled  resting  spores,  although  in  a  few  genera,  or  subdivisions 
of  genera,  they  may  germinate  immediately.  Germination  con- 
sists in  the  production  of  a  promycelium  (basidium-like),  which  is 
generally  divided  into  four  cells,  from  each  of  which  arises  on  a 
sterigma  a  small  thin-walled  spore,  a  sporidium  (basidiospore). 

The  sporidia  germinate  promptly  under  favorable  conditions 
and  may  immediately  penetrate  the  host.  The  mycelium  de- 
veloped from  this  infection  may  give  rise  to  aecidia  and  spermo- 
gonia,  uredospores  and  teleutospores,  teleutospores  alone,  etc. 


PROTOBASIDIOMYCETES  387 

Heteroecism.  In  this  order  of  fungi  there  has  been  developed 
not  only  great  diversity  in  form  and  character  of  spores,  and  in  the 
relationships  of  these  types  one  to  another,  but  also  a  very  definite 
relationship  between  the  different  spore  types  and  the  host  plants. 
Where  more  than  a  single  spore  type  is  present  a  species  may 
either  complete  its  entire  life  cycle  upon  a  single  host,  that  is, 
produce  all  spore  forms  in  its  life  cycle  on  one  host,  or  it  may 
require  two  plants  for  complete  development  (in  a  few  cases 
three)  in  regular  order.  The  former  group  of  rust  fungi  are 
termed  autcecious  and  the  latter  hetercecwus.  Autcecism  is  the 
rule  among  fungi  generally.  Heteroecism  is  better  developed  in 
rusts  than  in  any  other  group  of  living  organisms,  and  it  is  with 
one  or  two  exceptions  confined  to  the  rusts,  so  far  as  the  fungi 
are  concerned.  There  are  more  than  150  cases  of  hetercecism 
which  have  been  experimentally  demonstrated  in  this  order,  and 
this  number  will  be  greatly  increased  as  the  experimental  work 
proceeds.  Upon  such  hosts  as  the  grasses,  sedges,  rushes  (Gram- 
ineae,  Cyperaceae,  Juncaceae),  and  allied  plants,  the  spore  forms 
produced  are  quite  generally  the  uredo  and  teleuto  stages,  or  one 
or  the  other  of  these  ;  and  in  general,  so  far  as  the  experimental 
work  has  been  carried,  such  fungi  have  other  stages,  at  least  an 
aecidial  stage,  upon  some  dicotyledonous  host.  Indeed,  in  only 
one  group  of  cases  (the  species  of  Puccinia  on  Phalaris)  is  the 
aecidial  stage  produced  on  another  monocotyledonous  host.  Again, 
in  no  case  of  hetercecism  has  the  aecidiospore  been  found  to  be 
capable  of  infecting  also  the  host  upon  which  it  is  borne.  Since 
the  teleutospore  germinates  by  the  development  of  a  promycelium 
and  sporidia,  and  in  no  other  manner,  it  is  precluded  that  the 
teleutospore  may  infect  directly  the  host  upon  which  it  is  pro- 
duced. The  uredospores  alone  possess  this  capacity. 

In  general,  it  would  seem  that  the  period  of  incubation  may 
vary  from  eight  to  twenty  days  during  the  growing  season,  for 
most  of  the  species  of  rusts.  The  time,  however,  will  vary  in  the 
same  species  under  different  climatic  conditions. 

The  terminology  of  spore  combinations.  Based  upon  the  asso- 
ciation of  spore  forms,  that  is,  upon  the  number  and  kind  of  spores 
present  in  a  particular  species,  Schroeter  has  proposed  certain  very 
convenient  type  names  as  below.  First,  however,  it  should  be  stated 


388  FUNGOUS  DISEASES   OF  PLANTS 

that  the  spermogonial,  aecidial,  uredo,  and  teleuto  stages  are  respec- 
tively represented  by  O,  I,  II,  III,  and  it  is  here  unnecessary  to 
consider  the  fifth  or  sporidial  stage  ;  the  types,  then,  are  as  follows  : 

Eu  forms  with  all  stages;  or  O,  I,  II,  III  present. 

Brachy  forms  with  aecidia  omitted;  or  O,  II,  III  present. 

Opsis  forms  with  uredo  omitted;  or  O,  I,  III  present. 

Hemi  forms  with  spermogonia  and  aecidia  omitted  ;  or  II,  III  present. 

Micro  forms  with  teleutospores  only;  or  III  present,  germinating  only 
after  a  resting  period. 

Lepto  v forms  with  teleutospores  only;  or  III  present,  germinating  im- 
mediately. 

It  is  interesting  to  note  that  in  the  far  North  or  in  Alpine 
regions,  as  Fischer  shows,  the  micro  and  lepto  forms  predominate. 
^Ecidia  occur  alone  in  considerable  number,  and  also  hemi  forms. 
Many  hemi  forms,  particularly  in  such  genera  as  Uromyces  and 
Puccinia,  have  been  insufficiently  investigated,  and  will  doubtless 
prove  to  be  eu  forms,  mostly  hetercecious,  that  is,  eu-hetero  forms. 

No  terms  applicable  alike  to  all  genera  having  similar  spore 
forms,  based  upon  some  common  root  and  the  prefixes  above 
mentioned,  expressing  also  hetercecism  and  autcecism,  have  been 
suggested.  It  seems  desirable  for  many  reasons  to  employ  as  this 
root  the  word  uredo>  and  since  it  will  be  used  in  combination  with 
these  prefixes,  there  can  scarcely  be  any  confusion,  although  uredo 
is  a  form-genus  name.  With  this  nomenclature  a  form  which  is 
eu-hetercecious  will  be  termed  euheterouredo,  and  the  other  combi- 
nations will  be  made  in  an  analogous  manner. 

II.    FAMILIES  AND   GENERA 

According  to  Fischer  the  order  may  be  most  conveniently  sub- 
divided into  four  families,  and  the  characters  employed  as  a  basis 
of  this  system  of  classification  are  for  the  most  part  those  of  the 
teleutospores.1 

1  Arthur  has  proposed  for  the  Uredinales  an  entirely  new  system  of  classifica- 
tion (Resultats  scientifiques  du  Congres  International  de  Botanique,  Vienne,  1905, 
pp.  331-348).  By  this  system  many  more  genera  would  be  constituted  since,  in 
addition  to  the  usual  characters,  the  completeness  of  the  life  cycle  with  respect 
to  the  four  main  stages  is  made  generically  diagnostic.  He  has  also  introduced 
the  terms pycnium,  cecium,  uredinium,  and  telium  in  substitution,  for  spermogonialj 
l,  uredo,  and  teleuto  stages. 


PROTOBASIDIOMYCETES  389 

1.  Pucciniaceae.    The  teleutospores  usually  consist  of  a  single 
cell  or  a  vertical  row,  sometimes,  however,  united  into  the  form  of 
a  relatively  small  head.    The  spores  are  borne  on  a  simple  or  com- 
pound pedicel.  The  uredospores  are  single,  on  hyaline,  deciduous 
pedicels.    The  aecidia  are  generally  provided  with  a  well-developed 
peridium.    The  genera  here  considered  are  Uromyces,  Puccinia, 
Gymnosporangium,  Gymnoconia,  Phragmidium. 

2.  Cronartiaceae.    The  teleutospores  are  without  pedicels,  and 
they  originate  in  chains,  or  series,  more  or  less  free  at  maturity,  or 
united  into  complex  bodies.    Chrysomyxa  and  Cronartium  are  the 
important  genera. 

3.  Coleosporiaceae.    The  teleutospores  are  united  into  a  layer 
generally  wax-like  in  texture,  and  orange-red  in  color.    The  spores 
are  generally  without  pedicels,  at  first  unicellular,  but  soon  dividing 
into  four  cells,  that  is,  to  form  the  promycelium  within  the  spore, 
each  cell  of  which,  therefore,  produces  a  sterigma  and  basidiospore. 
The  genus  Coleosporium  includes  the  more  important  species. 

4.  Melampsoraceae.    The  teleutospores  form  a  closely  adherent 
crust-like  layer,  each  cell  of  which  germinates  by  a  typical  promy- 
celium.   The  uredospores  are  borne  singly,  and  the  aecidia  are  with 
or  without  peridia.    Melampsora  is  the  chief  genus. 

The  genera  above  mentioned  may  be  briefly  described  as  follows  : 

Uromyces.  The  teleutospores  are  unicellular  with  a  terminal 
germ  pore  ;  the  uredospores  are  generally  provided  with  many  evi- 
dent germ  pores  ;  the  aecidia  are  provided  with  peridia,  the  aecidio- 
spores  are  without  germ  pores,  and  the  spermogonia  are  spherical 
with  minute  circular  ostiola. 

Puccinia.  This  genus  is  similar  to  Uromyces  except  that  the 
teleutospores  are  two  celled.  Unicellular  teleutospores  may  also 
occur  in  some  species. 

Gymnosporangium.  The  teleutospores  are  commonly  two  celled, 
exceptionally  three  or  four  in  a  row.  They  are  borne  in  pustules ; 
and,  at  maturity,  owing  to  the  development  of  substances  resulting 
partially  from  the  gelatinization  of  the  long  pedicels,  they  are 
pushed  out  into  jelly-like  masses,  sometimes  horn-like  in  form. 
The  spores  are  often  provided  with  several  germ  pores  arising 
near  the  side  wall,  though  apical  germ  pores  may  be  present. 
There  are  no  uredospores,  and  the  aecidia  (rcestelia)  are  often 


390  FUNGOUS  DISEASES  OF  PLANTS 

jug-shaped  or .  cylindrical,  with  thick-walled  peridia.  The  aecidio- 
spores  are  highly  colored,  and  possess  numerous  germ  pores. 
They  are  invariably  accompanied  by  flask-shaped  spermogonia. 

Gymnoconia.  This  genus  resembles  Puccinia  in  the  general 
characters  of  the  teleutospore,  and  no  uredospores  are  present. 
The  most  abundant  spore  form  is  that  of  the  caeoma  stage.  The 
latter  is  an  aecidium  without  a  peridium,  the  spores  being  borne  in 
chains ;  and  in  this  case  the  spores  are  generally  highly  colored, 
orange  to  orange-yellow.  The  spermogonia  are  numerous,  spherical, 
and  very  simple  in  form. 

Phragmidium.  The  teleutospores  are  made  up  of  three  or  more 
cells  in  a  row  borne  upon  a  persistent  pedicel.  Uredospores  are 
present,  and  these  are  borne  in  pustules  bordered  by  paraphyses  ; 
each  spore  possesses  several  germ  pores.  The  aecidia  are  also  of 
the  caeoma  type,  but  here  there  is  an  outer  border  of  unicellular, 
curved  paraphyses.  The  spermogonia  are  flat  or  discoidal.  Species 
of  this  genus  occur  only  upon  Rosaceae. 

Chrysomyxa  forms  a  teleutosporic  cushion,  the  cells  of  which 
are  closely  adherent.  These  spores  germinate  immediately  by  the 
production  of  a  promycelium.  The  uredospores  are  borne  in  chains, 
as  are  also  the  aecidiospores,  the  two  kinds  being  more  or  less 
similar.  The  aecidia,  however,  are  provided  with  well-developed 
peridia. 

^Cronartium  is  characterized  by  teleutospores  united  into  a  cylin- 
drical column,  each  spore  germinating  immediately  by  the  pro- 
duction of  a  promycelium  from  near  the  apex.  The  uredospores 
are  borne  singly  on  pedicels  within  a  semispherical  body  possess- 
ing a  differentiated  peridium.  This  latter  structure  is  provided  with 
a  small  terminal  pore  or  mouth. 

Coleosporium.  In  this  genus  the  teleutospores  are  closely 
adherent,  with  a  rounded,  thickened,  gelatinizing  apex.  The 
sterigmata  are  long,  and  the  sporidia  large,  ovate,  and  flattened. 
The  spore,  at  first  a  single  cell,  divides  to  produce  a  series  of  four 
inner  promycelial  cells. 

Melampsora.  The  teleutospores  are  generally  unicellular  and 
closely  united  into  indefinite  crusts.  The  uredospores  are  borne 
singly,  often  interspersed  with  paraphyses.  The  aecidia  are  of  the 
caeoma  type,  and  paraphyses  are  occasionally  present. 


PROTOBASIDIOMYCETES 


391 


III.    SYNOPSIS   OF  SPECIES 

Arranging  the  species  here  discussed,  together  with  a  few  others 
as  examples,  in  groups  according  to  the  spore  forms  and  heterce- 
cism  or  autoecism,  we  have  the  following : 


Euautouredo  (Stages  O,  I,  II,  III) 

Uromyces     appendiculatus     (Pers.) 

Lev 

Uromyces  Trifolii  (Hedw.)  LeV. . 


Uromyces  Betes  (Pers.)  Tul.     .     .     . 

Puccinia  Asparagi  De  C 

Puccinia  Helianthi  Schw. 
Puccinia  Violce  (Schum.)  De  C.  . 

Puccinia  Menthce  Pers 

Gymnoconia       Peckiana       (Howe) 

Tranz 

Phragmidium      subcorticium 

(Schrank)  Wint 


HOSTS 

Phaseolus  vulgaris  (beans)  (also  species 

of  Dolichos  and  Lablab.) 
Trifolium  hybridum,  T.  incarnatum,  T. 

pratense,    T.    repens,    etc.   (various 

clovers) 

Beta  vulgaris  (wild  and  cultivated  beet) 
Asparagus  officinalis  (asparagus),  etc. 
Helianthus  annuus  (sunflower),  etc. 
Viola  spp.  (violets) 
Certain  Labiatae  (mints) 

Rubus  occidentalis  (blackberry),  etc. 
Rosa  spp.  (various  roses) 


Euheterouredo  (Stages  O,  I,  II,  III) 

O,  I 
Euphorbia  Cyparissias 


HOSTS 


Uromyces  Pisi  (Pers.) 
De  Bary. 

Puccinia  graminis  Pers. 


Puccinia    Sorghi    Schw. 
Puccinia    Phlei-pratensis 

Eriks.  &  Henn. 
Puccinia  rubigo-vera 

DeC. 
Puccinia     Pruni-spinosce 

Pers, 


Berberis  vulgaris 

(barberry) 
Berberis  Lycium 

Berberis  Aquifolium 


Oxalis  cymosa  (oxalis) 


Boraginaceae 

Hepatica  acutiloba 
(hepatica) 


II,  III 

Pisum  sativum  (pea) 
Lathyrus    pratens"is, 
etc. 

Avena  sativa  (oats) 

Hordeum  vulgare 

(barley) 

Secale  cereale  (rye) 
Triticum  vulgare 

(wheat) 

Zea  mays  (Indian  corn) 
Phleum  pratense 

(timothy),  etc. 
Triticum    spp.,  Avena 

sativa,  etc. 
Prunus  spp.  (plum, 

peach) 


392  FUNGOUS  DISEASES  OF  PLANTS 

Chrysomyxa  Rhododendri      Picea  excelsa  Rhododendron  ferrugi- 

(De  C.)  De  Bary  (Norway  spruce)  neum 

R.  hirsutum 
Cronartium      Ribicola          Pinus   strobus  (white        Ribes  spp.  (currant, 

Fisch.  de  Waldh.  pine)  gooseberry) 

Coleosporium    Senecionis      Pinus  sylvestris  Senecio  vulgaris 

Pers.  (Scotch  pine)  S.  sylvaticus 

S.  viscosus,  etc. 

Melampsora  tremulcz^ul.       Pinus  sylvestris  Populus  tremula 

(Scotch  pine)  (poplar) 

Opsiautouredo  (Stages  O,  I,  III) 

HOSTS 
Puccinia  Tragopogi  Pers Tragopogon  spp.  (salsify) 

Opsiheterouredo  (Stages  O,  I,  III) 

HOSTS 
O,  I  III 

Gymnosporangium    ma-        Pyrus  Malus  (apple)  Juniperus  virginiana 
cropus  Lk.  (red  cedar) 

Pyrus   coronaria  (wild  J.  virginiana  (red  cedar) 

crab) 

Gymnosporangium  globo-      Pyrus  Malus  (apple)  J.  virginiana  (red  cedar) 
sum  Farl. 

Pyrus  communis  J.  virginiana  (red  cedar) 

(pear) 

Pyrus  americana  J.  virginiana  (red  cedar) 

Cydonia  vulgaris  J.  virginiana  (red  cedar) 

(quince) 

Gymnosporangium  Sabi-      Pyrus  communis  J.  Sabina 

na  (Dicks.)  Wint.  (pear) 

Gymnosporangium  clava-      Crataegus  tomentosa  J.  communis  (common 
riceforme  (Jacq.)  Rees  Juniper) 


Brachyautouredo  (Stages  O,  II,  III) 

HOSTS 

Pucc'inia  Hieracii  (Schum.)  Mart.     .     Hieracium  spp. 

Puccinia  suaveolens  (Pers.)  Rostr.   .     Cirsium  arvense  (Canada  thistle) 

Hemiuredo  (Stages  II,  III) 

HOSTS 

Uromyces  Caryophyllinus  (Schrank; 

Wint Dianthus  Caryophyllus  (carnation),  etc. 

Uromyces  scutellatus  (Schr.)  Wint.     Euphorbia  spp.  (spurges) 


PROTOBASIDIOMYCETES  393 

Uromyces  Rumicis  (Schum.)  Wint.  Rumex  spp.  (sorrels) 

Hemileia  vastatrix  Berk.  &  Br.  .     .  Coffea  arabica  (coffee) 

Puccinia  Chrysanthemi  Roze.     .     .  Chrysanthemum  spp. 

Puccinia  Polygon*  Pers Polygonum  spp. 

Puccinia  Allii  De  C Allium  Cepa  (onion) 

Microuredo  (Stage  III) 

Uromyces  Solidagmts(Somm.}N\zss\.     Solidago  spp.  (goldenrod) 

Puccinia  Ribis  De  C Ribes  spp.  (currant,  gooseberry) 

Puccinia  fusca  Relhan Anemone  nemorosa,  etc. 

Leptouredo  (Stage  III)  . 

Puccinia  malvacearum  Mont.     .     .     Althaea  rosea  (hollyhock),  etc. 
Puccinia  Xanthii  Schw Xanthium  spp.  (cocklebur) 

(Stages  O,  III) 
Uromyces  tepperianus  Sacc.   .     .     .     Acacia  spp. 

(Stages  O,  I) 

elatinujn  Alb.  &  Schw.     .     Abies  spp.  (firs) 
Grossularice  Schum.    .     .     Ribes  spp.  (currant,  gooseberry) 
Peridermium  Engelmannii  Thiim.      Pinus  Engelmannii 

(Stage  II) 

Uredo  Fid  Cact Ficus  carica  (fig) 

Uredo  Gossypii  Sager Gossypium  hirsutum  (cotton),  etc. 

During  the  past  few  years  considerable  activity  has  been  mani- 
fest in  the  study  of  the  cytology  and  possible  fertilization  processes 
in  the  Uredinales.  It  had  been  known  since  the  studies  of  Sappin- 
Trouffy  and  Dangeard  that  the  binucleate  condition  of  the  teleuto- 
spore  and  of  the  mycelium  preceding  it  leads  finally  to  a  fusion  of 
these  two  nuclei  preceding  the  development  of  the  promycelium. 
The  recent  studies  have  been  directed  primarily  toward  a  knowl- 
edge of  the  origin  of  this  binucleate  condition.  Blackman  in  some 
extensive  studies  of  a  caeoma  stage,  in  particular,  demonstrated  what 
he  believed  to  be  a  fusion  phenomenon  in  the  following  manner : 
During  the  early  development  of  this  stage  numerous  gametic 
branches  arise.  These  come  in  contact  in  pairs,  the  older  and 


394 


FUNGOUS   DISEASES  OF  PLANTS 


larger  branch  cutting  off  an  apical  cell.  The  smaller  gamete  in 
time  loses  its  nucleus  by  migration  through  a  pore  into  the  larger 
gamete,  and  the  cells  thus  provided  with  two  nuclei  become  each 
properly  the  basal  cell  of  one  of  the  chains  of  spores  which  arise 
in  this  type,  corresponding  to  the  aecidium,  each  spore  of  which 


J. 


FIG.  194.   PHRAGMIDIUM  SPECIOSUM:  DEVELOPMENT  OF  ^CIDIOSPORES 
(After  Christman) 

a,  progametes ;  &,  gamete  and  sterile  cell ;  c,  after  gametic  fusion  and  nuclear 
division  ;  d  and  e,  spore  production 

possesses  paired  nuclei.  He  would  also  homologize  the  apical  cell 
of  the  larger  gamete  with  the  trichogyne  of  certain  lower  plants,  and 
would  assume  that  in  the  phylogeny  of  these  plants  the  spermatia 
were  functionally  in  connection  with  this  organ.  The  work  of 
Christman  and  Olive  on  this  and  other  rust  fungi  in  part  confirm 
Blackman's  results.  They  are  also  able  to  identify  the  gametes,  but 
the  communication  between  these  two  adjacent  cells  is  generally. 


PROTOBASIDIOMYCETES  395 

however,  effected  by  a  dissolution  of  the  upper  portion  of  the  cell 
walls  in  contact,  thus  securing  a  union  of  two  cells.  From  these 
united  cells,  with  two  nuclei,  as  a  basal  structure  arise  the  chain  of 
spores  as  before.  The  evidence  offered  seems  to  thoroughly  explain 
the  origin  of  the  binucleate  condition.  While  there  are  many 
exceptions  which  might  be  noted,  there  is  in  general,  in  the  case 
of  a  species  showing  all  spore  types,  the  following  nuclear  life 
history.  The  mycelium  which  produces  the  spermogonia  and  the 
aecidium  is  uninucleate.  There  is  a  fusion  of  cells  in  the  aecidium 
(where  such  organ  is  present)  and  the  aecidiospores  are  binucleate. 
The  mycelium  which  produces  the  uredospores  and  the  teleuto- 
spores  is.  binucleate,  and  these  spores  are  themselves  binucleate 
(in  this  type).  Fusion  of  the  nuclei  results  at  about  the  time  of  ger- 
mination of  the  teleutospore,  so  that  the  sporidia  are  uninucleate. 
It  is,  however,  unnecessary  here  to  enter  into  a  more  detailed  dis- 
cussion of  these  phenomena. 

IV.    CLOVER  RUST 
Uromyces  Trifolii  (Hedw.)  Lev. 

HOWELL,  J.  K.    The  Clover  Rust.    Cornell  Agl.  Exp.   Sta.  Built.  24:    129- 

139.    1890. 
PAMMEL,  L.  H.    Clover  Rust     Iowa  Agl.  Exp.  Sta.  Built.  13:  51-55.    1891. 

Habitat  relations.  The  clover  rust  is  ordinarily  a  common 
disease  of  various  species  of  Trifolium.  It  causes  a  disease  of  the 
clovers  more  serious  in  many  instances  than  that  produced  by 
Pseudopeziza,  already  mentioned.  The  Uromyces  is  cosmopolitan, 
and  the  more  susceptible  hosts  are  important  forage  plants.  Among 
the  clovers  the  following  species  are  frequently  infested  :  red  clover 
(Trifolium  pratense),  hybrid  clover  (Trifolium  hybridum),  white 
clover  (Trifolium  repens),  and  crimson  clover  (Trifolium  incar- 
natum).  The  prevalence  of  the  disease  apparently  varies  greatly 
with  the  season,  and  is  to  a  considerable  extent  determined  by  the 
spring  conditions.  We  have,  however,  no  very  accurate  knowledge 
of  the  climatic  relations  of  this  fungus. 

This  fungus  is  taken  as  a  type  of  an  autoecious  member  of  the 
genus,  as  it  may  have  all  stages  on  the  same  host  plant.  The 
various  stages  commonly  occur  upon  Trifolium  repens  and  also 


FUNGOUS  DISEASES  OF  PLANTS 


upon  Tvifolium  carolinianum,  much  less  frequently,  however,  upon 
some  of  the  other  species  mentioned.  In  general,  the  spermogonial 
and  aecidial  stages  are  not  commonly  found  upon  the  red  clover, 
the  host  upon  which  the  other  stages  are  perhaps  most  frequent. 

Nevertheless,  the  reported 
absence  of  aecidial  stages 
upon  this  host  in  certain 
regions  may  be  due  to  the 
fact  that  careful  examina- 
tions have  not  been  made 
at  the  proper  season. 

The  fungus.  The  my- 
celium corresponds  very 
closely  to  that  described 
as  generally  characteristic 
of  the  whole  order.  It  is 
considered  to  be  local. 
The  spermogonia  and 
aecidia  generally  appear 
during  very  early  spring 
or  at  almost  any  time  dur- 
ing open  winter.  They 
occur  upon  the  under  sur- 
faces of  the  leaves  and  on 
the  petioles.  The  aecidio- 
spores  (14-23/4  in  diam- 
eter) germinate  readily  in 
water,  and  under  favor- 
able conditions  infection 
in  the  greenhouse  or  in 
the  open  may  be  secured, 
with  the  production  of  uredosori  within  two  weeks.  The  uredo- 
spores,  as  shown  in  Fig.  195,  d,  measure  about  22-26  x  18-20/4. 
These  spores  also  germinate  readily,  and  repeated  crops  of  the 
uredospores  may  be  produced,  possibly  in  some  cases  extending 
into  the  winter,  and  even  carrying  the  fungus  through  the  year. 
Teleutospores  are  produced,  however,  and  these  may  occur  in 
sori  with  uredospores,  or  in  independent  sori,  as  the  season 


FIG.  195.   UROMYCES  TRIFOLII:  CLOVER  RUST 


PROTOBASIDIOMYCETES  397 

advances.  These  spores  are  20-35  X  I5~22At>  and  a  spore  ger- 
minates by  the  production  of  the  characteristic  promycelium,  di- 
vided ordinarily  into  four  cells,  each  producing  its  sporidium.  The 
germination  of  the  teleutospore  would  seem  to  take  place  ordinarily 
several  weeks  prior  to  the  appearance  of  the  spermogonium  and 
aecidium,  both  of  which  arise  only  from  teleutosporic  infection. 
The  failure  of  the  spermogonia  and  aecidia  on  red  clover,  pre- 
viously referred  to,  may  also  indicate  that  the  teleutosporic  form 
does  not  so  readily  infect  this  species  of  host. 


FIG.  196.    UROMYCES  APPENDICULATUS:  RUST  OF  BEANS.    (Photograph  by 
H.  H.  Whetzel) 

As  a  rule,  control  measures  seem  to  be  unnecessary ;  at  any  rate 
no  practical  preventive  methods  are  known. 

V.    RUST  OF  BEANS 
Uromyces  appendiculatus  (Pers.)  L^v. 

DE  BARY,  A.  Recherches  sur  le  deVeloppement  de  quelques  champignons 
parasites.  Ann.  d.  Sci.  nat.  Bot.  (SeV.  4)  20:  68-99.  1863. 

WHETZEL,  H.  H.  Bean  Rust.  Cornell  Agl.  Exp.  Sta.  Built.  239 :  298-299. 
figs.  113-113.  1906. 

This  fungus  is  widely  distributed,  occurring  on  the  bean  (Phaseo- 
lus  vulgaris)  and  other  related  species.  It  is  also  reported  in  south- 
ern latitudes  on  relatives  of  the  cowpea,  such  as  Dolichos  ornatus, 


398  FUNGOUS  DISEASES  OF  PLANTS 

Lab  lab  vulgaris,  Vigna  marginata,  etc.  The  fungus  commonly 
appears  late  in  the  season,  and  it  is  often  destructive  to  foliage, 
causing  early  maturity  and  lessened  production  of  the  beans.  There 
is  great  difference  in  susceptibility  of  varieties  both  among  dwarf 
and  pole  sorts.  Moreover,  the  fungus  is  harbored  by  the  old  leaves 
and  vines.  Burning  these  would  reduce  the  quantity  another  year. 
The  effect  of  turning  under  affected  parts  does  not  seem  to  have 
been  tested.  Selection  of  resistant  varieties  would  seem  to  be 
possible  for  each  locality.  The  spermogonia  and  aecidia  are  very 
light  in  color.  The  aecidiospores  are  colorless  and  polyhedral, 
17-32  x  14-23/4;  the  obovate,  minutely  echinulate  uredospores, 
which  are  24-33  X  16-20/4,  occur  in  rather  minute  sori ;  and  the 
teleutospores  are  broadly  elliptical,  measuring  26-35  X  20-26/4, 
and  each  spore  is  .provided  with  a  large,  terminal  papilla. 


VI.    RUST  OF  VETCH  AND  GARDEN  PEA 
Uromyces  Pisi  (Pers.)  De  Bary 

DE  BARY,  A.    Recherches  sur  le  deVeloppement  de  quelques  champignons 

parasites.    Ann.  d.  Sci.  nat.  Bot.  (Sdr.  4)  20:   68-99.    l863- 
KLEBAHN,  H.    Die  wirtswechselden  Rostpilze,  I.e.,  p.  330. 

In  the  United  States  this  species  is  not  so  prevalent  as  the  pre- 
ceding species.  It  shows,  however,  an  interesting  hetercecism.  The 
pycnidia  and  aecidia  occur  on  Euphorbia  Cyparissias,  while  the 
uredospores  and  teleutospores  are  found  upon  Lathyrus  pratensis, 
Vicia  cracca,  Pisum  sativum,  and  Pisum  arvense.  In  addition,  a 
number  of  other  hosts  have  been  given  for  stages  II  and  III.  In 
this  rust  the  aecidia  and  spermogonia  are  together  irregularly  dis- 
tributed on  the  under  surfaces  of  the  leaves.  The  aecidia  are 
numerous,  with  deeply  cleft  peridia,  the  cells  of  which  have  a  very 
slight  lumen.  The  aecidiospores  are  more  or  less  isodiametric,  and 
from  1 8  to  22  /4  in  diameter.  The  spore  wall  is  decorated  with  fine 
wart-like  projections.  The  uredosori  are  small,  pulverulent,  and 
distributed  over  the  leaf.  The  uredospores  are  more  or  less  spher- 
ical, and  measure  21-25/4.  The  wall  is  thick  and  the  4-5  germ 
pores  are  evident.  The  teleutospores  are  obovate,  with  short,  hya- 
line stalks.  The  wall  is  uniformly  thickened  and  beset  with  fine 
warts,  except  at  the  apex,  where  there  is  a  conspicuous,  flat  papilla. 


PROTOBASIDIOMYCETES  399 

VII.    BEET    RUST 
Uromyces  Beta  (Pers.)  Tul. 

KUHN,  J.    Der  Rost  der  Runkelriibenblatter,  Uromyces  Beta.    Bot.  Zeitg.  27  : 

540-544.    1869. 
MCALPINE,  D.    The  Rusts  of  Australia,  /.  c.,  Uromyces  beta  (Pers).  Kiihn., 

1  00-101.  pi.  17,  figs.  148-149;  pi.  43,  fig.  316;  pi.  H. 

The  spermogonia  occur  in  small,  yellowish  groups,  and  the  aecidia 
in  similarly  colored  but  somewhat  larger  spots,  within  which  they 
may  be  arranged  in  circular  or  regular  form.  The  aecidia  are 
saucer-shaped  and  white,  the  aecidiospores  more  or  less  isodiametric, 
1  7-36  fjL  in  diameter,  with  orange-colored  contents.  Both  the  uredo 
and  the  teleuto  stages  occur  in  sori  irregularly  distributed  over  the 
surfaces  of  the  leaf,  often  circularly  disposed.  The  uredospores  are 
mostly  obovate,  21-24  *  35At-  The  walls  are  provided  with  some- 
what distant  echinulations  and  two  opposite  germ  pores.  The 
teleutospores  are  similarly  obovate,  18-24  X  25~32At-  The  wall  is 
scarcely  thicker  at  the  apex,  with  an  apical  germ  pore,  and  a  very 
distinct  papilla  of  the  same  diameter  as  the  germ  pore.  The 
pedicel  is  short  and  persistent.  This  fungus  is  prevalent  in 
Australia,  and  it  is  not  uncommon  in  Europe  ;  but  in  the  United 
States  it  appears  only  to  have  been  observed  in  California.  This 
species  is  found  on  cultivated  beets  (Beta  vulgaris\  also  on  wild 
species  of  this  genus.  According  to  the  observations  of  Kiihn  the 
mycelium  may  be  biennial  in  the  host,  forming  aecidia  practically 
throughout  the  year. 

VIII.    CARNATION  RUST 

Uromyces  Caryophyllinus  (Schrank)  Wint. 

ATKINSON,  GEORGE  F.   Carnation  Diseases.  Amer.  Florist  8  :  720-728.  figs. 


STEWART,  F.  C.    Combating  Carnation  Rust.    N.  Y.  (Geneva)  Agl.  Exp.  Sta. 

Rept.  15:  461-495.    1895.    (Also  Built.  100.) 
STUART,  WM.    Some  Studies  upon  Carnation  Rust.    Vermont  Agl.  Exp.  Sta. 

Rept.  8  :    115-118.    1894. 

Occurrence  and  effects.  The  fungus  causing  carnation  rust  was 
recognized  in  Europe  more  than  a  century  ago,  and  it  was  properly 
named  during  the  first  half  of  the  nineteenth  century.  It  has  long 
been  recognized  as  a  common  disease  of  the  carnation  (Dianthiis 


4oo 


FUNGOUS  DISEASES  OF  PLANTS 


Caryophyllus],  and  it  occurs  also  upon  other  species  of  this  genus, 
and  upon  some  other  related  genera.  Prior  to  1 890  it  had  not  been 
noted  in  the  United  States,  and  it  is  doubtful  if  it  was  previously 
common.  Since  that  time,  however,  it  has  rapidly  spread  through- 
out the  regions  where  carnations  are  grown  either  under  glass  or 
in  the  open.  For  a  few  years  after  its  abundant  appearance  in  this 
country  it  threatened  to  cause  a  panic  in  carnation  growing,  and 
florists'  magazines  and  papers  devoted  much  space  to  a  discussion 
of  the  disease,  methods  of  control,  susceptibility  of  varieties,  etc. 


FIG.  197.    CARNATION  RUST 

It  is  now  permanently  established  as  one  of  the  regularly  antici- 
pated diseases  of  the  carnation,  but  there  is  no  fear  that  its  pres- 
ence in  any  way  jeopardizes  carnation  growing  as  an  industry,  at 
least  so  far  as  the  best  growers  are  concerned. 

Host  resistance.  Since  the  appearance  of  this  pest  there  has 
been  opportunity  for  selection,  so  that  resistant  varieties  might 
be  secured,  or  at  least  so  that  the  more  susceptible  sorts  might 
be  discarded,  particularly  when  more  or  less  similar  varieties 
may  be  grown  which  are  less  sensitive.  Perhaps  no  commercial 
variety  of  this  plant  has  proved  more  susceptible  to  the  rust  than 
the  Scott.  The  susceptibility  of  this  variety  seemed  to  be  intensi- 
fied the  longer  it  was  in  the  trade.  The  Jubilee  (scarlet)  and 
Flora  Hill  (white)  have  also  proved  susceptible,  and  these  have 


PROTOBASIDIOMYCETES 


401 


been  to  a  very  considerable  extent  discarded  by  growers  who  can- 
not handle  the  plant  so  as  to  prevent  rust.  On  the  other  hand, 
varieties  like  the  Enchantress  (daybreak  pink)  and  Lawson  (pink) 
have  under  a  variety  of  conditions  demonstrated  a  high  degree  of 
resistance.  Nevertheless,  the  conditions  under  which  the  plants 
are  grown  affects  to  a  considerable  extent  the  amount  of  the  rust. 
Of  two  growers  using  cuttings  from  the  same  stock  with  different 
regard  for  sanitation  and  different  methods  of  cultivation,  the  one 
may  find  the  rust  abundant  in  his  houses,  and  the  other  may  be 
able  to  grow  plants  practically  free  from  it.  It  is  certain  that  poor 
ventilation  and  conditions  permitting  the  deposit  or  retention  of 
drops  of  water  upon  the  surfaces  of  the  leaves  is  more  conducive 
to  the  spread  of  the  fungus,  but  its  approximate  relations  to 
environmental  factors  have  not  been  determined. 

The  fungus.  The  life  history  of  this  fungus  is  incompletely 
known.  The  uredosporic  stage  is  the  common  method  of  propaga- 
tion, but  the  teleutosporic  stage  may  also  be  found  under  the  condi- 
tions of  greenhouse  or  garden.  The  uredospores  are  more  or  less 
spherical  or  ellipsoidal  in  form,  ordinarily  varying  from  24-35x21- 
26  p.  The  cell  wall  is  thick  and  sparsely  beset  with  minute  spines. 
The  uredosporic  pustules  are  pulverulent,  light  chestnut  brown  in 
color,  and  may  be  found  upon  leaves  or  stems.  The  teleutospores 
are  not  dissimilar  in  form  to  the  uredospores,  and  are  commonly 
ellipsoidal,  varying  from  20-35x18-25^.  The  rather  uniformly 
thickened  chestnut  brown  membrane  is  marked  by  minute  wart- 
like  markings  best  seen  in  the  dry  condition.  The  spores  possess 
terminal  germ  pores  marked  by  a  papillate,  hyaline  covering.  The 
pedicels  are  short  and  colorless.  The  uredospores  germinate  read- 
ily in  water,  and  the  experiments  made  by  Stewart  indicate  that 
they  are  unusually  resistant  to  many  fungicides  and  toxic  agents. 
A  solution  of  1-500  copper  sulfate  was  required  to  give  inhibition 
of  germination,  and  a  still  stronger  solution  to  entirely  prevent 
germination.  On  the  other  hand,  potassium  sulfide  i-iooo  pre- 
vented germination,  and  even  weaker  solutions  inhibited  consider- 
ably this  process. 

It  would  appear  that  the  mycelium  is  not  greatly  localized 
in  the  host,  but  no  accurate  determination  of  this  point  can  be 
cited.  Furthermore,  few  inoculation  experiments  have  been  made 


402  FUNGOUS  DISEASES  OF  PLANTS 

in  order  to  determine  the  possibility  of  spreading  the  disease 
to  vigorous  adult  plants.  Observation  would  indicate  that  adult 
plants  may  be  affected,  and  consequently  that  the  disease  may  be 
spread  rapidly  during  the  growing  season.  In  fact,  it  is  only  upon 
this  basis  that  the  rapid  spread  of  the  fungus  can  be  accounted 
for.  Yet  there  is  very  little  experimental  data  upon  which  to  rely 
for  confirmation  of  this  statement. 

Control.  Three  methods  of  control  have  been  considered  and, 
when  necessary,  practiced,  and  these  in  addition  to  a  maintenance 
of  the  best  general  conditions  of  the  environment  with  respect  to 
sanitation.  In  the  first  place,  resistant  varieties  should  be  grown 
as  far  as  possible.  Secondly,  it  is  desirable,  where  the  rust 
abounds,  or  where  rust-susceptible  varieties  must  be  grown,  to 
have  simple  V-shaped  wire  mesh  supports  placed  between  the  rows 
in  order  to  hold  the  foliage  away  from  the  moist  soil,  and  also  to 
permit  of  watering  without  constant  wetting  of  the  leaf  surfaces. 
Thirdly,  it  may  be  necessary  to  employ  fungicides  when  other 
methods  fail.  In  such  cases  the  plants  may  be  sprayed  once  each 
week  with  a  solution  of  copper  sulfate  about  1-500  (i  Ib.  copper 
sulfate  to  12-15  gallons  of  water),  or  with  a  solution  of  potassium 
sulfide  i  ounce  to  I  gallon. 

IX.  UROMYCES:  OTHER  SPECIES 

Uromyces  scutellatus  (Schr.)  Wint.  apparently  occurs  as  a  very 
common  parasite  of  a  large  number  of  species  of  Euphorbia.  The 
species  is  ordinarily  broken  up  into  different  forms,  which  vary  very 
slightly  one  from  another  in  general  appearance  and  considerably 
in  extreme  size,  the  uredospores  being  17-35  X  I4-23AtJ  and  the 
teleutospores  20-38  x  16-25/1.  Whether  this  fungus  is,  in  any  of 
its  forms,  a  euheterouredo,  or  invariably  a  hemiuredo,  as  it  appears 
to  be,  is  not  definitely  determined. 

Uromyces  Rumicis  (Schum)  Wint.  This  species  is  found  on 
many  members  of  the  genus  Rumex.  It  appears  to  be  a 
hemiuredo. 

Uromyces  Solidaginis  (Somm.)  Niessl.  This  is  commonly  con- 
sidered to  be  a  microuredo  and  occurs  upon  several  species  of 
Solidago. 


PROTOBASIDIOMYCETES 


403 


X.    ASPARAGUS  RUST 
Puccinia  Asparagi  De  C. 

HALSTED,  B.  D.    The  Asparagus  Rust;  Its  Treatment  and  Natural  Enemies. 

N.  J.  Agl.  Exp.  Sta.  Built.  129:    1-20.  pi.  1-2.    1898. 
HALSTED,  B.  D.    Experiments  with  Asparagus  Rust.    N.  J.  Agl.  Exp.  Sta. 

Kept.  11:  343-347-    1898. 
SIRRIXE,  F.  A.    Spraying  for  Asparagus  Rust.    N.  Y.  Agl.  Exp.  Sta.  Built. 

188:    122-166.    1900. 
SMITH,  RALPH  E.    The  Water-Relation  of  Puccinia  Asparagi.    Bot.  Gaz.  38 : 

19-43.  figs.  1-2 1.    1904. 
SMITH,  RALPH  E.   Further  Experience  in  Asparagus  Rust  Control.    Calif.  Agl. 

Exp.  Sta.  Built.  172 :    1-22.    1906. 
SMITH,  RALPH  E.    Asparagus  and  Asparagus  Rust  in  California.    Calif.  Agl. 

Exp.  Sta.  Built.  165:   1-95.  Jigs.  1-45.    1905. 
STONE,  G.  E.,  and  SMITH,  R.  E.    The  Asparagus  Rust  in  Massachusetts.   Mass. 

(Hatch)  Agl.  Exp.  Sta.  Built.  61 :   1-20.    1899. 


Distribution  and  general 
effects.  The  fungus  caus- 
ing asparagus  rust  was  de- 
scribed a  century  ago,  and 
the  effects  of  this  fungus 
upon  the  asparagus  plant 
have  been  known  perhaps 
almost  as  long  by  growers 
in  Europe.  It  has  been, 
however,  in  general  of 
no  great  consequence  as 
an  asparagus  disease;  but 
upon  making  its  appear- 
ance in  America,  some- 
what more  than  twelve 
years  ago,  this  rust  began, 
under  our  conditions,  im- 
mediately to  assume  an 
unexpected  importance. 
In  a  brief  space  of  time 
the  asparagus-growing 
interests  of  the  country  were  seriously  threatened.  According 
to  Halsted,  who  followed  closely  its  early  spread  in  this  country, 
it  became  in  1896  a  serious  pest  in  New  Jersey,  Delaware, 


FIG.  198.   PUCCINIA  ASPARAGI:  RUST  OF 
ASPARAGUS 


404  FUNGOUS  DISEASES  OF  PLANTS 

Long  Island,  and  parts  of  New  England.  In  succeeding  years 
it  became  more  serious  in  those  sections,  and  spread  also  rapidly 
southward  and  westward.  It  has,  however,  varied  greatly  in 
destructiveness  in  the  eastern  states  from  year  to  year,  but  on 
the  whole  the  asparagus  industry  suffered  such  a  check  that  a 
much  more  complete  study  has  been  made  of  methods  of  culture, 
of  direct  means  of  control,  and  of  varietal  resistance.  As  a  result, 
in  the  East  the  asparagus  interests  have  been  gradually  adapted  to 
the  new  conditions,  and  it  is  not  likely  that  the  former  epidemics 
have  left  any  very  serious  impression  upon  this  product  as  grown 
for  immediate  marketing. 

In  1901  the  rust  seems  to  have  been  of  the  first  serious  conse- 
quence in  southern  California,  spreading  northward,  and  doing  the 
greatest  damage  up  to  about  1905,  since  which  time  the  energetic 
control  measures  suggested  by  Smith  have  been  effective  with  the 
best  growers  in  many  localities. 

Climatological  relations.  It  has  been  demonstrated  that  the 
prevalence  of  asparagus  rust  in  most  localities  bears  a  very  definite 
relation  to  climatological  and  other  conditions.  When  the  air  re- 
mains dry  throughout  the  summer,  rust  is  very  largely  prevented. 
Occasional  rains  with  intervening  periods  of  low  humidity  do  not 
constitute  favorable  conditions  for  the  fungus.  A  heavy  formation 
of  dew  is  almost  inevitably  requisite  to  the  abundance  and  spread 
of  the  disease.  This  latter  is  of  much  practical  importance  in  Cali- 
fornia, and  referring  to  the  conditions  in  that  state,  Smith  says, 
"The  amount  of  rust  varies  directly  and  exactly  with  the  amount  of 
dew,  and  so  long  as  there  is  little  or  no  dew,  there  can  be  no  rust." 

Again,  on  light  soil  which  has  a  tendency  to  dry  out  during 
the  growing  season,  rust  is  prevailingly  worse  than  on  land 
where  the  plant  secures  the  amount  of  moisture  needed  by  the 
roots.  The  greater  susceptibility  on  such  lands  has  been  attributed 
to  the  reduced  vigor  of  the  host  plant,  but  here  also  a  dew  relation 
may  often  be  a  possible  factor.  Nevertheless,  good  cultivation  is 
favorable  to  the  host  plant,  as  innumerable  experiments  have 
demonstrated.  It  should  further  be  noted  that  the  asparagus 
under  half  shade  is  commonly  free  from  rust. 

Host  plants.  Among  the  varieties  of  asparagus  commonly  grown 
in  the  United  States,  the  Palmetto  has  proved  most  resistant,  this 


PROTOBASIDIOMYCETES 


405 


resistance  being  particularly  noticeable  when  the  varieties  are  grown 
side  by  side  for  a  period  of  years.  The  final  effect  of  the  rust 
upon  the  plant  from  year  to  year  is  a  determining  factor  in  adapt- 
ability. Sirrine  was  unable  to  confirm  the  observations  as  to  the 
high  resistance  of  the  Palmetto  as  grown  on  Long  Island,  but 
it  is  suggested  that  a  weaker  strain  is  there  in  use.  Conover's 
Colossal  and  the  various  forms  related  to  this,  or  the  selections 
from  it,  are  types  of  the  more  susceptible  sorts.  These,  moreover, 
are  the  varieties  upon  which  the 
canning  industry  depends.  The 
fungus  also  occurs  on  some  wild 
species  of  asparagus  such  as  As- 
paragus capsicus  and  Asparagus 
maritimus. 

The  spore  forms.  No  impor- 
tant distortions  are  made  upon 
the  host  by  different  stages  of 
this  fungus.  All  spore  forms 
are  produced  on  stems  and 
twigs  (Fig.  198),  and  the  uredo 
and  teleuto  stages  occur  also 
on  the  leaf-like  branches.  The 
aecidial  stage  may  appear  at 
almost  any  point  in  the  United 

States  with  a  growing  season  no  shorter  than  that  of  northern 
New  Jersey.  The  secidia  appear  in  rather  long,  light  green, 
cushion-like  areas.  They  are  short-cylindrical,  with  a  white  perid- 
ium,  and  the  spores  appear  orange  colored  from  the  contents ; 
the  wall,  however,  is  hyaline  and  granulose.  The  spores  meas-. 
ure  i  5- 1 8  ^  in  diameter.  They  may  germinate  immediately,  and 
when  dry,  some  at  least  retain  the  capacity  for  germination 
throughout  several  weeks.  Penetration  of  the  host  plant  is  ap- 
parently through  the  stomata.  The  spermogonia  appear  in  small 
yellow  clusters. 

The  uredo  or  red  rust  stage  appears  in  early  summer,  or  shortly 
after  the  aecidial  stage,  at  first  in  scattered,  deep  brown  sori,  but 
afterwards  the  latter  may  be  confluent.  The  uredospores  are  yel- 
lowish brown,  with  thick  walls,  fine  yellow  markings,  and  provided 


FIG.  199.   PUCCINI  A  ASPARAGI: 
TELEUTOSPORIC  SORUS 


406  FUNGOUS  DISEASES  OF  PLANTS 

with  four  germ  pores.  They  measure  21-24/1.  They  are  produced 
in  such  abundance  as  to  be  dusted  in  quantity  upon  any  passing 
object  or  taken  in  clouds  by  the  wind  for  some  distance.  They 
are  unquestionably  the  chief  means  of  distributing  the  disease 
during  the  growing  season.  It  has  been  found  (Smith)  that  their 
vitality  upon  drying  is  not  retained  for  more  than  a  few  months. 

The  black  rust  stage  appears  later  in  the  season,  apparently  as- 
the  conditions  for  uredosporic  formation  become  unfavorable.  The 
sori  are  black-brown,  and  while  for  a  time  protected  by  the  epi- 
dermis, they  are  finally  exposed.  The  teleutospores  are  elliptical, 
slightly  constricted,  as  a  rule,  and  measure  30-60  x  21-28  /x.  The 
wall  is  thick  at  the  apex,  and  the  pedicels  very  long.  These  spores 
show  a  more  or  less  persistent  attachment  to  the  host.  Unicellular 
teleutospores  also  occur.  They  have  been  germinated  towards  the 
middle  or  end  of  winter,  with  the  characteristic  promycelium  and 
sporidia.  It  is  believed  that  the  general  infection  in  cultivated 
fields  each  season  results  from  aecidiospores  produced  on  wild  or 
escaped  plants,  and  not  directly  from  the  germination  of  teleuto- 
spores which  have  remained  in  or  about  the  soil. 

Control.  The  numerous  attempts  which  have  been  made  to 
control  the  asparagus  rust  by  means  of  Bordeaux  mixture  have 
been  more  or  less  unsuccessful.  Nevertheless,  Sirrine,  in  experi- 
ments on  Long  Island,  and  later  others  have  used  to  advantage 
a  Bordeaux  prepared  with  resin.  The  mixture  which  may  be 
recommended  is  as  follows  : 

Bordeaux  mixture,  5-5-40  formula,  40  gals. 
Resin  mixture,  2  gals.,  diluted  to  10  gals. 

The  resin  preparation  consists  of  resin,  5  Ibs. ;  potash  lye,  I  Ib. ;  fish  oil,  i  pt. ; 
and  water,  5  gals. 

In  California  it  has  been  found  that  under  certain  climatic  con- 
ditions thorough  spraying  with  sulfur,  either  as  dust  or  liquid,  is 
an  efficient  preventive,  the  prevention  resulting  from  the  fumes. 
In  any  case,  however,  where  control'  consists  in  the  use  of  sprays, 
provision  should  be  made  for  the  best  circulation  of  air  possible, 
that  is,  the  field  should  be  as  free  from  obstructions  around  the 
border,  and  the  rows  should  be  a  sufficient  distance  apart  so  as 
not  to  make  the  conditions  any  more  favorable  than  possible  for 
high  moisture  content  of  the  air.  Thorough  cultivation  should  be 


PROTOBASIDIOMYCETES  407 

given,  and  requisite  irrigation  is  desirable  when  there  is  a  tend- 
ency for  drying  out  to  affect  the  health  of  the  plant  during  the 
summer.  It  would  appear,  however,  that  the  best  method  of  con- 
trolling the  fungus  is  by  the  selection  of  resistant  sorts.  Since  the 
Palmetto  variety  has  shown  itself  fairly  resistant  in  the  East,  it  is 
probable  that  other  sorts  may  be  obtained  which  will  possess  some 
of  the  desirable  qualities  of  the  Conover,  with  the  resistance  of 
the  Palmetto.  So  far  as  I  am  aware,  no  extensive  report  has 
been  made  upon  the  resistance  of  European  varieties  under  our 
conditions. 

XI.    VIOLET  RUST 
Pucdnia  Violce  (Schum.)  De  C. 

ARTHUR,  J.  C.,  and  HOLWAY,  E.  W.  D.    Violet  Rusts  of  North  America. 
Minn.  Bot.  Studies  Built.  (Ser.)  2:  631-641.    1901. 

This  species  of  violet  rust  is  parasitic  on  about  sixty  different 
hosts  in  the  genus  Viola  throughout  North  America  and  parts  of 
South  America,  also  Europe  and  Asia.  The  spermogonia  and 
aecidia  occur  early  in  the  season  in  light  brown  spots  scattered 
over  leaves  and  stalks.  The  aecidiospores  are  ovoidal,  16-24  x 
i  o- 1 8  IJL.  The  uredospores  and  teleutospores  follow  in  succession, 
both  of  these  on  the  under  surfaces  of  the  leaves,  producing  no 
definite  spots ;  yet  a  large  number  of  sori  may  become  confluent 
so  as  to  present  the  appearance  of  dark  brown  areas.  The  fungus 
is  not  of  much  consequence  from  an  economic  point  of  view  in 
relation  to  violet  culture,  but  it  is,  nevertheless,  the  most  common 
of  the  five  (assuming  the  validity  of  some  species)  violet  rusts. 

XII.    MINT  RUST 
Pucdnia  Menthce  Pers. 

This  is  a  species  apparently  well  distributed  throughout  a  large 
part  of  the  world  on  about  thirty-five  members  of  the  mint  family. 
The  fungus  is  closely  related  to  a  number  of  other  species  whose 
host  plants  are  also  certain  mints.  In  fact,  more  than. thirty  species 
of  rusts  have  been  described  upon  the  various  mints,  and  the  studies 
that  have  thus  far  been  made  upon  these  indicate  an  interesting 
evolution  of  the  parasitic  forms.  The  species  referred  to,  however, 


408  FUNGOUS  DISEASES  OF  PLANTS 

is  one  of  the  most  common,  yet  it  may  not  be  considered  of  any 
special  economic  importance.  The  aecidiospores  are  almost  twice 
as  long  as  broad,  40  x  1 7-26  //,.  The  uredospores  are  subspherical, 
and  the  teleutospores  are  conspicuous  by  their  long,  hyaline,  and 
relatively  thick  pedicels,  papillate  apex,  red-brown  color,  and  verru- 
cose  outer  wall. 


FIG.  200.   ^CIDIAL  STAGE  OF  THE  GRAIN  RUST  ON  BARBERRY 

XIII.    BLACK  RUST  OF  GRAIN 
Pucrinia  graminis  Pers. 

BOLLEY,  H.  L.,  and  PRITCHARD,  F.  J.    Rust  Problems.    N.  Dak.  Agl.  Exp. 

Sta.  Built.  68:  607-672.  figs.  1-30.    1906. 
CARLETON,  M.  A.    Cereal  Rusts  of  the  United  States.    Div.  Veg.  Phys.  and 

Path.,  U.  S.  Dept.  Agl.  Built.  16:   1-73.  pis.  1-4.    1899. 
DE  BARY,  A.    Neue  Unters.  iiber  die  Uredineen,  insb.  d.  Entw.  der  Puccinia 

graminis  u.  d.  Zusammenhang  desselben  mit  Aecidium  Berberidis.  Monats- 

ber.  K.  Akad.  d.  Univ.  Berlin  (1865):    15-49.  pi.  n. 
ERIKSSON,  J.    Neue  Unters.  iiber  d.  specialisirung  Verbreitung  u.  Herkunft 

des   Schwarzrostes  (Puccinia  graminis  Pers.)  Jahrb.   f.  wiss.    Bot.  29 : 

499-524.    1896. 

ERIKSSON,  J.,  und  HENNING,  E.    Die  Getreideroste,  /.  c. 
McALPiNE,  D.    The  Life-history  of  the  Rust  of  Wheat.    Dept.  Agl.  Victoria 

Built.  14:    1891. 
OLIVE,  E.  W.    Rusts  of  Cereals.    S.  Dak.  Agl.  Exp.  Sta.  Built.  109:   1-20. 

figs.  1-5.    1908. 

WARD,  H.  MARSHALL.    Illustrations  of  the  Structure  and  Life-history  of  Puc- 
cinia graminis,  the  fungus  causing  the  "  Rust "  of  Wheat.    Ann.  Bot.  2 : 

217-222.  fits.  //,  12.    1 8$8, 


PROTOBASIDIOMYCETES 


409 


Probably  the  most  important  species  of  the  rust  family,  both 
from  an  economic,  point  of  view  and  also  from  the  point  of  view 
of  the  development  of  mycological  research,  is  the  common  species, 
Puccinia  graminis,  upon  cereals.  It  was  upon  this  species  that 
the  classical  researches  of.De  Bary  (1865  et  seq.)  were  based, 
throwing  light  upon  many  phenomena  of  parasitism.  In  more 
recent  times  this  species  has 
served  further  as  a  means  of 
developing  a  knowledge  of 
biological  and  physiological 
forms,  or  specialized  races.  It 
has  been  the  means,  also,  of 
showing  the  relation  of  the 
summer  spore,  or  uredo  stages, 
to  the  continual  propagation  of 
certain  rust  forms,  and  Eriks- 
son's mycoplasm  theory  sought 
evidence  in  phenomena  ob- 
served in  this  species. 

Distribution  and  occurrence. 
It  would  appear  that  this  fungus 
is  distributed,  in  one  or  more 
of  its  numerous  forms  or  races, 
throughout  the  world  wherever 
certain  grasses  may  be  found. 
It  is  not  in  all  regions  the  most  common  cereal  rust,  but  in 
general  it  is  so  considered.  The  economic  work  upon  rust  fungi 
in  such  widely  separated  and  important  cereal-growing  countries 
of  the  world  as  Australia,  Russia,  Western  Europe,  and  the 
United  States  has  been  largely  concerned  with  this  species.  It  is 
therefore  the  fungus  which  is  commonly  known  as  rust  of  wheat, 
oats,  barley,  and  other  cereals  and  many  grasses.  It  is  not  at  all 
restricted  by  minor  climatic  conditions,  and  in  the  United  States 
it  is  found  in  its  various  forms  upon  certain  grasses  from  the 
moist  Atlantic  seaboard  to  the  most  arid  portions  of  the  Great 
Plains,  and  from  the  Gulf  Coast  to  the  Great  Lakes.  The  annual 
losses  throughout  the  world  amount  to  a  stupendous  figure,  often 
estimated  to  reach  one  hundred  million  dollars, 


FIG.  201.    RUST  OF  OATS 


410  FUNGOUS  DISEASES  OF  PLANTS 

Host  plants.  It  is  scarcely  possible  to  indicate  all  the  various 
hosts  upon  which  the  species,  in  its  various  forms,  has  been  re- 
ported. As  mentioned  above,  however,  it  attacks  all  the  more 
important  cereals,  —  wheat,  oats,  rye,  and  barley,  —  together  with 
ordinary  grasses  belonging  to  the  same  genera,  in  addition  to  such 
economic  forms  as  species  of  Dactylis,  Alopecurus,  Agrostis,  Poa, 
Phleum,  Festuca,  and  numerous  others. 

The  important  forms  or  physiological  races  of  this  species 
which  have  been  thus  far  well  established  through  experimental 
study  are  as  follows  : 

1.  Secalis  Eriks.  &  Henn.     On  Secale  cereale,  Hordeum  vul- 
gare,  Agropyrum  repens,  Elymus  arenarius,  Bromus  secalimis, 
and  other  hosts. 

2.  Avenae  Eriks.  &  Henn.    Occurring  on   several  species  of 
A  vena   (including  cultivated   oats),   Agrostis   scabra,   A  lope -cunts 
pratensis,  Dactylis  glomerata,  and  other  grasses.    Nevertheless, 
there  is  some  disagreement  about  some  of  the  hosts  upon  which 
this  form  has  been  reported. 

3.  Tritici  Eriks.  &  Henn.    On  several  species  of  Triticum  (cul- 
tivated wheats),  Hordeum,  Agropyrum,  and  Elymus ;   also  some 
other  grasses. 

4.  Agrostis  Eriks.  On  Agrostis  canina  and  Agrostis  stolonifera. 

5.  Airae  Eriks.  &  Henn. 

6.  Poae  Eriks.  &  Henn.  on  Poa  compressa.   This  form,  however, 
requires  further  study  in  order  to  be  sure  that  it  is  not  more  prop- 
erly one  of  those  already  indicated. 

The  fungus.  This  species  is  of  the  type  euheterouredo.  The 
chief  alternate  host  throughout  its  usual  range  is  the  common  bar- 
berry (Berberis  vulgaiis).  The  life  history  of  the  fungus  may  be 
only  briefly  outlined,  beginning  with  its  appearance  upon  the  bar- 
berry in  the  form  of  the  spermogonial  and  cluster-cup  stages. 

The  mycelium  is  septate,  considerably  branched,  and  intercellu- 
lar. It  gives  rise,  however,  to  small,  very  slightly  differentiated 
haustoria,  which  penetrate  the  cells.  The  mycelium  is  distributed, 
in  the  case  of  the  barberry,  throughout  various  parts  of  the  leaf. 
It  is,  however,  in  every  case  localized  in  areas  within  a  definite 
range  of  the  point  of  infection.  In  the  development  of  the  spore 
stages  there  is  the  usual  sequence.  The  spermogonial  stage  appears 


PROTOBASIDIOMYCETES 


411 


first  as  small,  flask-shaped  bodies,  shown  in  Fig.  202,  breaking 
through  the  upper  epidermis  of  the  leaf.  Somewhat  later,  and 
in  the  same  spot,  there  appear  on  the  under  surface  the  aecidial 


FIG.  202.   PUCCINIA  GRAMINIS.    (After  Ward) 
a,  section  of  barberry  leaf  showing  spermogonia  and  aecidia ;  £,  aecidium 

stage,  which  breaks  through  the  epidermis  in  somewhat  similar 
manner.  The  spermogonium  shows  a  very  simple  development, 
resulting  by  the  gradual  growth  in  extent  of  a  small  mass  of  fila- 
mentous hyphae  developing  in  an  intercellular  manner  just  beneath 


412  FUNGOUS  DISEASES  OF  PLANTS 

the  upper  epidermis.  At  maturity  the  flask-shaped  body  consists 
of  an  indefinite  wall,  later  giving  rise  to  numerous  filamentous 
branches  within,  most  of  which  project  inward  toward  the  center, 
the  majority  bearing  on  their  tips  small  rod-shaped  or  oval  conidia. 
Other  filamentous  hyphae  emerge  from  the  mouth  of  the  pycnidium 
as  hair-like  processes.  The  hyphae  making  up  the  pycnidium  are 
all  tinted  yellow  or  orange  in  color,  the  coloring  matter  being  first 
present  in  the  protoplasm  and  later  deposited  in  the  cell  walls. 
The  spots  in  which  first  the  pycnidia  and  later  the  aecidia  are  pro- 
duced are  pale  yellowish  to  orange  in  color,  and  the  leaf  is  some- 
times considerably  thickened. 

The  aecidia  are  organized  in  the  mesophyll  tissue  near  the  lower 
epidermis.  In  general,  each  aecidium  is  differentiated  and  developed 
following  the  formation  of  a  weft  of  filamentous  hyphal  elements. 
According  to  Richards  there  is  first  formed  at  the  base  of  the 
hyphal  mass  a  well-differentiated  short,  thickened  hypha.  By  the 
division  of  this  hypha  there  arise  numerous  fertile  branches,  or 
young  conidiophores,  each  of  which  originates  a  chain  of  spores. 
Every  alternate  cell  in  the  chain  becomes  a  perfect  spore  ;  the 
others  are  small  and  temporary,  remaining  for  a  time  as  wedge- 
like  structures  between  the  spores.  The  outer  border,  or  inclosing 
layer,  consisting  of  differentiated  hyphae,  forms  a  definite  peridium. 
Prior  to  the  rupture  of  the  epidermis,  the  fruit  body  has  a  more 
or  less  spherical  form,  and  it  consists  merely  of  the  sheath,  or 
peridium,  inclosing  the  numerous  chains  of  spores.  The  increase 
in  size  of  the  spores  breaks  the  peridium  as  well  as  the  epidermis, 
and  the  aecidia  appear  superficially  in  the  cluster-cup  form  (Fig. 
202).  The  spores  there  exposed  separate  readily  and  are  dis- 
tributed. The  aecidiospores  are  more  or  less  spherical  and  vary 
from  14  to  26  11  in  diameter.  This  spore  germinates,  and  upon  the 
different  grass  hosts  it  penetrates  the  stomata,  producing  the  my- 
celium of  the  uredo  stage. 

The  uredosori  generally  occupy  linear  areas,  yet  upon  some 
hosts  they  may  be  in  the  form  of  small  circular  dots.  They  show 
a  considerable  amount  of  coloring  matter  when  young,  and  when 
mature  appear  yellowish  brown.  They  are  ovate,  10-15  x  20-35/4, 
with  rather  thick  walls,  the  outer  of  which  bears  numerous  echinu- 
lations  or  small  spine-like  appendages  (Fig.  203,  a).  There  are  four 


PROTOBASIDIOMYCETES 


413 


germ  pores  equatorially  disposed  and  opposite.  Upon  many  hosts 
the  uredospores  are  produced  throughout  a  very  long  season.  They 
may  appear  upon  grain  or  blue  grass  in  the  early  spring  before  the 
aecidiospore  may  be  developed  in  the  same  region.  In  many  cases 
it  is  evident  that  the  rust  may  be  propagated  from  year  to  year  by 
continuous  generations  of  the  uredospores.  Again,  it  has  been 
experimentally  shown  that  uredospores  may  retain  the  power  of 


FlG.  203.    PUCCINIA   GRAM1NIS:    UREDOSPORES    AND    TELEUTOSPORES 

germination  for  weeks.  It  is,  therefore,  generally  possible  to  ac- 
count for  the  appearance  of  rust,  even  in  spring  grain,  at  a  dis- 
tance from  the  alternate  barberry  host.  In  seeking  to  explain  the 
infections  in  spring  grain  as  due  to  the  uredo  stage  from  some 
neighboring  grass  stubble,  it  should  be  remembered  that  artificial 
inoculation  experiments  have  shown  a  very  definite  restriction  of 
hosts  in  the  different  physiological  species.  Some  who  have  fol- 
lowed carefully  outbreaks  of  rust  in  the  grain  fields,  year  after 
year  in  the  Northwest,  feel  that  the  problem  is  not  yet  completely 


414  FUNGOUS  DISEASES  OF  PLANTS 

solved.  The  rust  may  appear,  or  seem  to  appear,  in  constantly 
increasing  amount  in  a  field  repeatedly  grown  to  wheat,  other  con- 
ditions apparently  remaining  the  same,  yet  it  is  hardly  possible  to 
assume  that  wintered  uredospores  would  explain  such  cases. 

The  teleutosori  are  generally  disposed  in  a  linear  manner  on 
stems,  leaves,  and  floral  parts.  They  may  arise,  during  the  early 
part  of  the  season,  in  the  uredosorus,  but  as  the  plant  matures, 
teleutospores  alone  are  developed  ;  thus  the  black  rust  form  is  that 
most  evident  at  harvest  time  and  later  upon  the  stubble.  In  gen- 
eral, the  spores  are  somewhat  spindle-shaped,  or  somewhat  broader 
at  the  apex,  deep  brown  in  color,  with  a  persistent  pedicel  (Fig. 
203,  £).  They  measure  35-60  x  12-22  /z.  One-celled  spores  are 
occasionally  found.  The  teleutospores  will  not,  as  a  rule,  germi- 
nate with  any  degree  of  satisfaction  until  they  have  been  exposed 
to  outside  conditions  throughout  a  considerable  portion  of  the 
winter.  Germination  has,  however,  been  repeatedly  followed,  and 
in  moist  air  the  promycelium  is  typically  four-celled,  each  produc- 
ing upon  a  fairly  long  sterigma  the  single  sporidium  (Fig.  203,  b). 

XIV.    RUST  OF  MAIZE 

Puccinia  Sorghi  Schw. 
ARTHUR,  J.  C.    The  /Ecidium  of  Maize  Rust.    Bot  Gaz.  38:  64-67.    1904. 

It  is  generally  supposed  that  this  fungus  is  a  native  of  America, 
and  that  it  may  be  regarded,  so  to  speak,  as  an  original  corn  (Zea 
mays]  parasite.  It  is  now  certainly  widely  distributed  in  maize- 
growing  regions,  but  is  more  abundant  under  conditions  of  rela- 
tively high  temperature.  This  fungus  has  also  been  reported  on 
sorghum,  but  the  maize  fungus  is  distinct  from  Puccinia ptirpure a, 
now  common  in  the  southern  United  States  and  in  the  West  Indies 
on  certain  species  of  sorghum.  The  uredospores  are  large,  23-30 
X  22-267*,  and  the  teleutospores  are  smooth,  28-45  X  l2~l7fJLt 
with  a  rather  long  and  thick  pedicel. 

On  maize  the  rust  affects  particularly  the  leaves  and  leaf 
sheaths,  but  it  may  cause  considerable  damage  to  the  develop- 
ment of  the  tassels.  Nevertheless,  it  seldom  amounts  to  an 
epidemic,  and  consequently  has  not  received  attention  from  the 
standpoint  of  control,  or  of  varietal  selection  of  the  host. 


PROTOBASIDIOM  YCETES  4 1 5 

The  maize  fungus  has  recently  been  connected  with  an  ^Ecidium 
m  Oxalidis  Thiim.)  on  Oxalis,  so  that  its  heteroecism  is 
established.  This  aecidial  stage  has  seldom  been  found,  and  there 
is  reason  to  believe  that  the  uredo  stage  may  commonly  serve  to 
carry  the  fungus  over  winter. 


XV.    TIMOTHY  RUST 
Puccinia  Phlei-pratensis  Eriks.  &  Henn. 

ERIKSSON,  J.,  u.  HENNING,  E.  Die  Hauptresultate  einer  neuen  Untersuchung 
iiber  die  Getreideroste.  Zeitsch.  f.  Pflanzenkr.  4:  140-142.  1894. 

ERIKSSON,  J.  Ueber  die  Specialisirung  des  Parasitismus  bei  den  Getreiderost- 
pilzen.  Ber.  d.  deut.  Bot.  Ges.  12:  292-331  (cf.  309-316).  1894. 

KLEBAHN,  H.    Die  wirtswechselden  Rostpilze,  /.  c.,  pp.  235-236. 

Timothy  rust  is  common  in  Europe,  occasionally  damaging  to 
a  noticeable  extent  the  cultivated  timothy  (Phleum  pratense).  It 
also  occurs  upon  some  other  cultivated  and  native  grasses.  The 
fungus  is  unquestionably  closely  related  to  Puccinia  graminis,  if 
not  a  form  of  this  species.  It  is  reported  ineffective  in  producing 
the  cluster  cup  of  the  barberry.  During  the  past'  few  years  the 
timothy  rust  has  been  found  in  a  considerable  portion  of  the  east- 
ern United  States,  although  previously  it  had  not  been  noticed, 
at  least  to  any  practical  extent.  It  is  not  yet  positive  that  the  rust 
which  occurs  in  America  is  the  same  as  the  European  species.  It 
is  conceivable  that  the  cultivated  timothy  has  gradually  become  sus- 
ceptible to  another  form  of  Puccinia  graminis,  but  this  remains  to 
be  determined  by  careful  experimental  work.  The  European  rust 
has  not  been  connected  with  an  aecidial  stage,  and  it  has  been 
shown  that  the  uredospores  are  apparently  capable  of  wintering 
over,  and  therefore  the  disease  may  be  readily  reproduced  from 
season  to  season  without  an  aecidial  stage.  If  the  appearance  in 
America  means  a  sudden  introduction  and  rapid  spread  of  the 
European  rust,  much  damage  may  be  expected  from  it.  On  the 
other  hand,  it  may  have  been  parasitic  upon  timothy  for  some 
time  without  having  attracted  attention.  Experiments  made  by 
Eriksson  in  the  open  indicate  that  the  rusts  on  timothy  and 
meadow  fescue  are  readily  transferred  from  one  of  these  hosts 
to  the  other,  and  with  much  less  success  to  several  other  grasses 
employed  in  the  experiments. 


41 6  FUNGOUS  DISEASES  OF  PLANTS 

XVI.    BROWN  RUST  OF  WHEAT  AND  RYE 
Puccinia  rubigo-vera  De  C. 

ERIKSSON,  J.    Ueber  die  Specialisirung  des  Parasitismus  bei  den  Getreiderost- 

pilzen.    Ber.  d.  deut.  bot.  Ges.  12:   292-331.    1894. 
FREEMAN,  E.  M.    Experiments  on  the  Brown  Rust  of  Bromes  (Puccinia  dis- 

persa).    Ann.  Bot.  16:  487-494.    1902. 
WARD,  H.  M.    On  the  Relations  between  Host  and  Parasite  in  the  Bromes 

[etc.].   Ann.  Bot.  16:   233-315.    1902. 

Occurrence  and  nomenclature.  The  brown  rust  of  wheat  and 
rye  is  second  only  to  the  black  rust  in  economic  importance.  In 
consideration  of  the  detailed  account  of  the  black  rust  of  wheat 
and  other  cereals  and  grasses,  it  will  only  be  necessary  in  discuss- 
ing the  brown  rust  to  draw  attention  to  the  chief  points  of  interest 
by  way  of  comparison.  Puccinia  rubigo-vera  occurs  upon  a  variety 
of  grasses  besides  wheats  and  rye,  among  these  certain  species  of 
Bromus,  Lolium,  and  Elymus.  The  aecidial  stage  was  by  De  Bary 
determined  to  be  a  form  on  a  borage,  Anchusa  arvensis,  known 
to  occur  also  on  Anchusa  officinalis.  The  nomenclature  of  this 
rust  is  complex,  and  at  the  outset  it  may  be  said  that  Eriksson 
and  Henning  distinguish  under  the  above  name  two  species,  and 
they  have  abandoned  the  name  Puccinia  rubigo-vera  De  C.  One 
of  these  species  is  denoted  the  yellow  rust,  and  to  it  is  applied  an 
old  name,  Puccinia  glumarum  (Schm.).  The  other  species,  desig- 
nated brown  rust,  is  made  a  new  species  and  called  Puccinia  dis- 
persa.  The  last  named  is  found  by  inoculation  to  be  connected 
with  the  aecidium  on  the  borage  hosts,  while  Puccinia  glumarum 
is  without  known  aecidial  stage. 

At  any  rate,  these  forms  have  not  been  commonly  distinguished 
in  the  literature,  and  Puccinia  rtibigo-vera  has  been  reported 
almost  as  widespread  throughout  the  region  of  cereal  production 
as  the  black  rust.  In  the  United  States  it  is  often  unusually  abun- 
dant in  the  central  West.  Bolley  and  others  have  shown  that  this 
fungus  is  able  to  carry  itself  through  the  winter  by  means  of  more 
or  less  continuous  production  of  the  uredo  stage  and  by  the  my- 
celium in  the  leaves  of  winter  grain. 

The  aecidia  occur  upon  leaf  blades,  petioles,  stems,  and  calyx  of 
the  borage  hosts,  producing  rather  conspicuous,  bright  yellow, 
slightly  swollen  spots. 


PROTOBASIDIOMYCETES  417 

It  was  very  largely  in  characters  of  the  uredosori  and  uredo- 
spores  that  there  was  found  a  means  of  distinguishing  two  species, 
or  forms,  as  above  mentioned.  In  the  form  Puccinia  glumarum 
the  uredosori  are  described  as  lemon-yellow,  the  sori  united  into 
long  linear  areas,  while  in  the  other  form  the  sori  are  irregularly 
distributed  over  the  whole  surface  and  are  described  as  brown- 
ocher  in  appearance. 

The  teleutospores  form  sori  which  remain  covered  by  the  epi- 
dermis ;  the  one  form  is  said  to  occur  more  upon  leaf  sheaths  and 
stems,  and  the  other  upon  the  under  surfaces  of  the  leaves. 
Groups  of  teleutospores  are  arranged  in  fan-shaped  masses  sur- 
rounded by  closely  united,  bent  paraphyses.  The  spores  are 
broader  at  the  apex,  irregular  in  form,  more  or  less  angular, 
generally  30-50^  in  length,  and  the  upper  cell  14-24^  broad. 

Both  of  the  forms  here  mentioned  are  again  divisible  into 
several  physiological  races,  each  restricted  to  one  or  to  relatively 
few  hosts. 

XVII.    RUST  OF  STONE  FRUITS 
Puccinia  Pruni-spinosa  Pers. 

HOLWAY,  E.  W.  D.    North  Amer.  Uredinales  1 :  55-56.  figs.  83  a,  83  b. 
MCALPINE,  D.    Peach-  and  Plum-Leaf  Rust.    Victoria  Dept.  Agl.  Guides  to 

Growers  5:    1-8.    1891. 
SCRIBNER,  F.  L.    Leaf  Rust  of  the  Cherry,  etc.   U.  S.  Dept.  Agl.  Rept  (1887) : 

353-355-  pl-3- 

This  rust  occurs  throughout  a  considerable  portion  of  southern 
North  America.  It  is  also  found  in  Europe  and  Asia.  It  was  in- 
troduced into  Australia,  apparently,  somewhat  earlier  than  1883, 
and  is  now  considerably  distributed  on  that  continent. 

This  fungus  has  been  found  on  various  species  of  the  genus 
Prunus  in  the  central  and  southern  United  States.  It  is  reported 
upon  such  hosts  as  the  peach  (Prunus  Persicd) ;  some  of  the  native 
species  of  plum,  such  as  Prunus  americana  and  Prunus  domestica  ; 
and  on  certain  cherries,  especially  Prunus  serotina.  In  other  sec- 
tions of  the  world  it  has  also  been  noted  on  the  almond  (Prunus 
Amygdalus),  on  the  apricot  (Prunus  armeniaca\  and  many  other 
economic  species.  As  a  rule,  this  fungus  is  found  upon  the  leaves, 
but  it  occurs  also  upon  fruits  of  peach,  almond,  and  apricot,  and 
upon  the  stems  of  the  peach  under  certain  climatic  conditions.  No 


418  FUNGOUS  DISEASES  OF  PLANTS 

striking  discoloration  of  the  leaves  is  produced  at  first,  but  the 
great  number  of  sori  which  may  be  formed  eventually  give  a 
light  brown  color  to  the  leaf  before  it  falls.  Considerable  defo- 
liation may  result,  and  it  is  stated  that  a  shot-hole  effect  is 
sometimes  produced  upon  the  almond.  The  fungus  is  much  more 
destructive  in  relatively  moist,  warm  climates.  It  appears  gener- 
ally toward  midsummer,  but  the  most  severe  effects  are  commonly 
in  the  fall. 

It  has  recently  been  determined  that  the  aecidial  stage  of  this 
fungus  is  ALcidinm  punctatum.  Tranzschel  was  able  to  produce 
the  rust  by  inoculations  from  the  aecidium  above  mentioned  on 
Anemone  coronaria.  These  results  were  confirmed  by  Arthur 
with  the  aecidium  from  Hepatica  acutiloba.  This  aecidium  has  a 
perennial  mycelium  in  some  of  its  hosts,  so  that  this  stage  alone 
is  believed  to  perpetuate  itself. 

The  uredospores  occur  upon  all  hosts  of  the  genus  Prunus 
mentioned.  They  are  generally  hypophyllous,  minute,  cinnamon- 
brown,  and  may  be  so  numerous  as  practically  to  cover  the  entire 
leaf.  The  spores  are  light  brown,  generally  ovate  or  elliptical, 
with  thickened  apex.  They  are  thickly  verrucose  and  are  pro- 
vided with  from  two  to  three  equatorial  germ  pores.  They  measure 
20-36  x  1 4-20  fji.  Paraphyses  are  abundant.  Tranzschel  deter- 
mined that  uredospores  kept  over  winter  at  St.  Petersburg  were 
capable  of  germination  the  following  spring. 

The  teleutospores  generally  appear  in  small  groups  among  the 
uredospores  and  later  supplant  these  entirely.  The  pustules  are 
generally  pulverulent  and  chestnut-brown.  The  teleutospores  are 
from  very  light  to  reddish  brown  upon  the  different  hosts.  In 
general  form  they  are  elliptical,  deeply  constricted,  and  the  two 
cells  are  more  or  less  equal,  often  subspherical.  They  separate 
readily.  These  spores  are  provided  with  pointed  tubercles.  The 
spores  measure  32-44  x  20-26 /-i.  The  pedicels  are  slender,  hya- 
line, and  fragile.  The  lower  portions  of  these  become  agglutinated 
into  short  columnar  masses.  The  free  portion  of  each  pedicel  is 
usually  about  the  length  of  the  spore. 


PROTOBASIDIOMYCETES  419 

XVIII.    HOLLYHOCK  RUST 
Pucdnia  malvacearum  Mont. 

DUDLEY,  W.  R.    The   Hollyhock    Rust.     Cornell  Agl.  Exp.  Sta.  Built.  25 : 
154-155.    1890. 


FIG.  204.   PUCCINIA  MALyACEARUM:  RUST  OF  HOLLYHOCK.    (Photograph  by 

H.  H.  Whetzel) 

The  hollyhock  rust  is  known  to  infest  a  large  number  of  genera 
and  species  of  the  mallow  family  (Malvaceae).  It  is  at  present  widely 
distributed  throughout  a  large  portion  of  the  world,  and  is  in  the 
United  States  most  important  on  the  cultivated  hollyhock  (Alth<za 


420  FUNGOUS  DISEASES  OF  PLANTS 

rosea}.  The  fungus  is  apparently  a  native  of  Chile  and  was  not 
found  in  central  Europe  until  between  1873  and  1877.  It  was 
evidently  introduced  into  the  United  States  prior  to  1886  and 
has  received  special  attention  since  about  1890. 

On  the  hollyhock  the  fungus  commonly  occurs  in  such  quantity 
that  the  proper  development  and  normal  functions  of  the  leaves 
may  be  seriously  inhibited.  The  sori  are  most  abundant  on  the 
under  surfaces  of  the  leaves  (Fig.  204),  but  they  also  occur  upon 
other  parts.  They  are  at  first  small  and  circular  in  outline,  but 
may  become  confluent  over  considerable  areas. 

During  favorable  conditions  the  teleutospores  germinate  im- 
mediately, and  there  is  no  evidence  that  the  mycelium  is  gener- 
ally perennial.  Nevertheless,  Fischer  believes  that  in  temperate 
climates  the  wintering  over  is  ordinarily  effected  by  means  of 
teleutospores  which  fail  to  germinate  on  account  of  being  over- 
taken by  unfavorable  conditions.  The  spores  are  light  colored 
and  measure  I7-24X  3 5-63  ft.  They  are  often  spindle-shaped, 
and  the  pedicel  is  long,  frequently  from  100  to  130/4. 

This  disease  has  been  fairly  well  controlled  by  the  destruction 
of  diseased  portions  of  plants  and  by  spraying  with  Bordeaux 
mixture. 

XIX.    PUCCINIA:  OTHER  SPECIES 

Puccinia  Helianthi  Schw.  This  euautouredo  occurs  commonly 
upon  numerous  species  of  Helianthus,  including  the  sunflower 
(Helianthus  annuus}.  Recent  experiments  indicate  that  the  form 
on  Helianthus  tuberosus  is  at  least  physiologically  distinct,  and 
doubtless  the  species  may  be  broken  up  into  many  forms.  Puc- 
cinia Helianthi  (with  all  spore  stages)  is  distinguished  from  Puc- 
cinia Tanaceti,  a  related  but  apparently  imperfectly  known  species, 
by  the  smooth  apex  of  the  teleutospore  and  the  presence  of  only 
two  germ  pores  in  the  uredospores. 

Puccinia  coronata  Cda.  This  species  has  an  aecidial  stage  upon 
the  buckthorn  (Rhamnus).  At  maturity  the  groups  of  cluster  cups 
are  very  conspicuous  by  the  color  and  also  by  the  deformities.  The 
aecidiospores  measure  18-25  x  14-19^.  The  uredo  and  teleuto 
stages  are  common  upon  oats,  and  on  such  cultivated  grasses  as 
Dactylis  glomerata  and  Festuca  sylvatica.  The  uredosori  are 


PROTOBASIDIOMYCETES  42 1 

bright  yellow,  the  spores  ovate,  with  roughened  surfaces,  measur- 
ing 28-32  x  20-24 /x.  The  teleutosori  remain  covered  by  the  epi- 
dermis, and  the  spores  are  notably  distinctive  in  being  cuneate  in 
form,  with  several  horn-like  projections  on  the  thickened  apex,  and 
with  a  very  short  pedicel.  This  species  has  also  been  broken  up 
into  diverse  forms,  some  of  which  are  considered  distinct  species. 

Puccinia  Chrysanthemi  Roze.  The  chrysanthemum  rust1  has 
been  of  some  consequence  in  Europe  and  America  during  the 
past  fifteen  years.  It  was  common  in  Japan  at  a  much  earlier 
time.  The  principal  hosts  are  Chrysanthemum  indicum  and 
Chrysanthemum  sinense.  In  the  warmer  coastal  regions  of  Japan 
and  in  Europe  and  America  continuous  generations  of  uredo- 
spores  may  be  produced.  In  these  places  teleutospores  occur 
rarely.  When  they  occur,  mesospores  and  irregularly  formed 
uredospores  are  also  common.  In  the  cooler  portions  of  Japan 
teleutospores  are  commonly  found  in  the  autumn.  It  would  ap- 
pear that  uredospores  and  teleutospores  are  the  only  stages  in  the 
normal  life  cycle  of  this  species.  In  greenhouse  culture  this  rust 
is  generally  controlled  by  resistant  stock  and  care  in  watering. 

Puccinia  Tragopogi  (Pers.)  Cda.  This  species,  occurring  on 
members  of  the  genus  Tragopogon,  and  especially  on  the  culti- 
vated form,  Tragopogon  porrifolius,  is  not  uncommon  in  gardens 
where  salsify  is  annually  grown.  It  is  constantly  without  uredo- 
spores and  exhibits  the  anomalous  condition  of  producing  also 
unicellular  teleutospores.  There  is,  moreover,  great  variability  in 
the  size  of  this  spore  form. 

Puccinia  suaveolens  (Pers.)  Rostr.  The  characteristic  odor,  or 
aroma,  of  the  spermogonia  is  a  distinctive  peculiarity  of  this  species. 
It  is  considered  to  be  a  means  of  attracting  insects,  perhaps  for 
purposes  of  distribution.  It  will  be  recalled,  however,  that  the  sper- 
matia  are  not  known  to  be  at  present  effective  in  the  propagation 

1  Arthur,  J.  C.  Chrysanthemun  Rust.  Ind.  Agl.  Exp.  Sta.  Built.  85  :  143-150. 
1900. 

Jacky,  E.  Der  Chrysanthemum- Rost.  Zeitsch.  f.  Pflanzenkr.  10  :  132-142. 
1900. 

Kusano,  S.  Biology  of  the  Chrysanthemum- Rust.  Built.  Coll.  Agl.  Imp.  Univ. 
Tokyo  8  :  (reprint  i-io).  1908. 

Roze,  E.  Le  Puccinia  Chrysanthemi,  etc.  Bull,  de  la  Soc.  Myc.  de  France  16  : 
88-93.  1900. 


422  FUNGOUS  DISEASES  OF  PLANTS 

of  any  rust.  The  spermogonia  are  extremely  numerous,  cover- 
ing practically  both  surfaces  of  the  leaf,  while  the  uredo  and 
teleutosporic  sori  occur  on  the  under  surface  of  the  leaves  only. 
In  the  first  generation  the  sori  are  confluent,  but  in  the  second 
generation  distinct.  This  species  occurs  on  the  common  Canada 
thistle  (Cirsium  arvense).  Infection  from  the  teleutospores  pro- 
duces a  mycelium  which  deforms  the  host,  but  the  infection  from 
uredospores  produces  a  localized  mycelium.  These  differences  upon 
the  same  host  suggest  a  condition  which  may  be  regarded  as  bio- 
logically intermediate  between  true  autoecism  and  hetercecism. 

Puccinia  Hieracii  (Schum.)  Mart.  This  rust  occurs  on  various 
species  of  Hieracium,  and  from  the  observations  made  it  would 
also  appear  to  be  a  species  embracing  many  different  forms. 

Puccinia  fusca  Relhan.  This  rather  variable  species  is  parasitic 
upon  certain  anemones,  and  the  mycelium  has  been  experimentally, 
determined  to  be  perennial  in  the  host. 

XX.    GYMNOSPORANGIUM 

FARLOW,  W.  G.    Notes  on  Some  Species  of  Gymnosporangium  and  Chryso- 

myxa  in  the  United  States.   Proc.  Amer.  Acad.  Arts  and  Sci.  20 :  3 1 1-323. 

1885. 
FARLOW,W.  G.  The  Development  of  the  Gymnosporangia  of  the  United  States. 

Bot.  Gaz.  11 :  234-241.    1886. 
FARLOW,  W.  G.    The  Gymnosporangia  (Cedar-Apples)  of  the  United  States. 

Anniv.  Mem.  Boston  Soc.  Nat.  Hist.    38  pp.  2  pis.    1880. 
PAMMEL,  L.  H.    The  Cedar  Apple  Fungi  and  Apple  Rust  in  Iowa.    Iowa  Agl. 

Exp.  Sta.  Built.  84:    1-36.    1905. 
RICHARDS,  H.  M.    The   Uredo-stage  cf   Gymnosporangium.    Bot.  Gaz.  14  : 

211-216.  pi.  77.    1889. 
THAXTER,  R.    Notes  on  Cultures  of  Gymnosporangium  made  in  1887  and 

1888.    Bot.  Gaz.  14:    163-172.    1889. 
THAXTER,  R.     The    Conn.    Species    of    Gymnosporangium    (Cedar-Apples). 

Conn.  Agl.  Exp.  Sta.  Built.  107:   1-6.    1891. 

There  is,  perhaps,  no  genus  of  rust  fungi  comprising  several  or 
more  species  which  is  as  uniform  in  developmental  processes  as 
the  genus  Gymnosporangium.  Aside  from  a  direct  agreement  in 
the  sequence  of  spore  forms,  and  in  the  general  relations  of  these 
forms  one  to  another  in  the  different  species,  all  have  the  same 
spore  forms,  namely,  spermogonia,  aecidia,  and  teleutospores  ;  and 
in  the  different  species  the  same  spore  forms  appear  in  almost 
the  identical  season. 


PROTOBASIDIOMYCETES  423 

There  are  about  fifteen  species  of  these  fungi,  all  but  one  of 
which  have  the  aecidial  or  rust  stage  (Rcestella)  on  some  member 
of  the  tribe  Pomeae,  generally  apple,  pear,  or  crab  (Pyrus),  quince 
(Cydonia),  shad  bush  or  service  berry  (Amelanchier),  or  hawthorn 
(Crataegus).  The  teleutosporic  stage,  which  is  commonly  produced 
on  hypertrophied  parts  in  the  nature  of  "cedar  apples,"  witches' 
brooms,  and  other  deformities  of  the  host,  generally  occurs  upon 
one  of  the  species  of  red  cedar  or  juniper  (Juniperus) ;  only  two 
species  of  these  fungi  are  exceptions,  these  having  as  a  host  the 
related  genus  Cupressus.  These  fungi  are  of  economic  interest 


FIG.  205.   ^ECIDIAL  STAGE  OF  GYMNOSPORANGIUM  ON  FRUIT  OF  HAW 

because  of  the  injuries  to  fruits  and  leaves  of  the  Pomeae,  and 
not  as  a  rule  because  of  serious  injuries  to  the  coniferous  hosts. 

On  account  of  the  great  similarity  in  development,  the  general 
facts  of  life  history  import  may  be  collectively  presented.  More- 
over, since  in  the  order  of  season  the  teleutosporic  form  occurs 
first,  the  discussion  will  follow  this  plan. 

Soon  after  the  growing  season  begins,  and  following  a  warm 
rain,  there  will  be  found  protruded  from  the  cedar  apples,  or  from 
enlargements  on  the  twigs  of  other  conifers  mentioned,  gelatinous, 
orange-colored  spore  masses,  sometimes  horn-like,  and  again  almost 
shapeless.  These  masses  consist,  in  large  part,  of  orange-tinted 


4^4 


FUNGOUS  DISEASES  OF  PLANTS 


teleutospores  with  long,  gelatinizing  pedicels  (Fig.  206).  These 
teleutospores  germinate  immediately.  Three  promycelia  often 
arise  from  a  spore,  each  through  a  germ  pore  situated  near  the 
septum  between  the  two  cells.  The  promycelium  may  form  four 
sporidia  in  the  usual  manner,  and  these  sporidia 
cannot  reinfect  the  cedar.  They  may  apparently 
be  borne  long  distances  by  the  wind.  Moreover, 
they  are  produced  during  the  season  when  young 
leaves  and  fruits  are  abundant  on  the  apple, 
quince,  and  such  plants.  Falling  upon  the  con- 
genial host,  the  spore  immediately  germinates, 
and  infection  is  secured.  In  time  the  rust  stage 
of  the  fungus  appears.  This  stage  consists  of 
spermogonia  and  aecidia.  It  is  then  perhaps  mid- 
summer, and  the  abundant  aecidiospores  return 
the  fungus  to  the  conifer  host,  where  in  time  a 
gall  or  a  deformity  is  again  produced. 

The  rust  spots  on  the  pomaceous  hosts  appear 
at  first  as  clear  yellow  or  orange  areas,  slightly 
thickened  or  raised.  Soon  a  papillate  appearance 
indicates  the  presence  of  the  spermogonia  or  pyc- 
nidia,  which  are  all  of  a  characteristic,  simple 
type.  The  aecidia  follow  in  a  brief  period  on  the 
under  side  of  the  leaf,  or  covering  large  areas  on 
the  fruit  (Fig.  205).  The  aecidium  (rcestelia)  is  an 
organ  of  some  length,  appearing  cylindrical  or 
jug-shaped  after  emergence.  A  circular  orifice 
is  developed,  and  the  peridium  breaks  into  a 
characteristic  margin,  sometimes  fimbriate.  The  spores,  which 
are  produced  in  chains,  break  apart  when  mature.  They  also 
germinate  immediately. 

Control  consists  primarily  in  the  removal  of  the  cedars,  if  that 
is  practicable.  Attention  should  also  be  paid  to  the  resistance  of 
varieties  of  apples  grown.  It  is,  moreover,  of  some  value  to  spray 
with  the  standard  Bordeaux  mixture  at  about  the  time  of  ripening 
of  the  teleutospores. 


FIG.  206.   GYMNO- 
SPORANGWM    MA- 
CROPUS:    TELEU- 
TOSPORES 


PROTOBASIDIOMYCETES  425 

XXI.    CEDAR  APPLES  AND  APPLE  RUST 
Gymno  sporangium  macropus  Lk. 

This  is  one  of  the  most  widespread  and  economically  important 
of  this  genus.  It  produces  the  large  cedar  apples  on  Junipertis 
virginiana  (Fig.  207).  This  fungus  occurs  practically  throughout 


FIG.  207.    GYMNOSPORANGIUM  MACROPUS:  CEDAR  APPLE 

the  range  of  the  red  cedar  and  its  other  hosts.  The  secidial  stage 
occurs  on  the  apple  (Pyrus  Mains)  and  also  on  Pyrus  coronaria, 
and  was  originally  described  as  Rcestelia  Pyrata  (Schw.)  Thaxter. 
On  the  leaves  some  injury  is  done  to  these  plants  when  the 


426  FUNGOUS  DISEASES  OF  PLANTS 

infection  is  severe,  but  it  is  upon  the  fruit  that  the  fungus  be- 
comes, in  many  sections  of  the  United  States,  a  serious  disease.  It 
is  far  more  common  in  regions  of  considerable  humidity,  but  owing 
to  the  fact  that  teleutqspores  are  produced  during  wet  weather,  infec- 
tion is  usually  immediately  assured  upon  the  pomaceous  hosts  in 
the  vicinity.  The  fungus  has  been  noticeably  abundant  in  apple- 
growing  regions  in  the  eastern  Appalachians  and  in  the  South. 
Varieties  of  apples  differ  greatly  in  their  susceptibility.  In  the  far 
West,  crosses  between  the  wild  crab  apple  and  the  cultivated  species 
have  given  some  forms  peculiarly  susceptible.  The  gall  formation 
on  the  cedar  commonly  attains  a  diameter  greater  than  2  cm.,  and 
when  the  horn-like  gelatinous  sori  are  developed,  the  mass  from 
edge  to  edge  may  measure  8  cm.  The  teleutospores  are  46-60  x 
15-20/4. 

XXII.    GYMNOSPORANGIUM:  OTHER  SPECIES 

Gymnosporangium  clavariaeforme  (Jacq.)  Rees  is  a  species  un- 
usually abundant  in  the  northeastern  United  States.  The  teleuto- 
sporic  form  occurs  on  the  common  or  dwarf  juniper  (Juniperus 
commtmis).  Slight  enlargements  of  the  twig  are  produced,  and  the 
sori  are  orange-red  in  appearance.  In  America  the  aecidia  occur 
on  the  hawthorn  (Cratcegus  tomentosa),  while  in  Europe  they  are 
also  produced  upon  Cratcegus  oxyacanthay  Cratcegus  monogyna, 
Pyrus  communis,  and  occasionally  other  pomaceous  trees.  This 
species  is  apparently  not  so  fixed  in  its  specialization  with  respect 
to  hosts  for  the  secidial  stage  as  other  members  of  this  genus. 

Gymnosporangium  globosum  Farl.  This  species  produces  on 
the  red  cedar  (Juniperus  virginiand]  smaller  cedar  apples  than  the 
preceding,  and  they  are  also  distinguished  from  the  latter  by  the 
texture  of  the  gall,  the  deeper  color  of  the  spore  masses,  and  cer- 
tain spore  characters. 

This  fungus  is  a  chief  cause  of  the  apple  rust  of  the  New 
England  States,  and  the  rcestelia  stage  is  also  found  on  the  pear, 
quince,  and  some  varieties  of  mountain  ash. 

Gymnosporangium  Sabinae  Plowr.,  which  is  closely  related  to 
Gymnosporangium  globosum,  has  also  the  same  coniferous  host. 
The  secidial  stage  has  for  some  time  been  recognized  as  injurious 
to  pear  culture  in  Europe. 


PROTOBASIDIOMYCETES  427 

XXIII.    ORANGE  RUST  OF  RASPBERRY  AND  BLACKBERRY 
Gymnoconia  Peckiana  (Howe)  Tranz. 

CLINTON,  G.  P.    Orange  Rust  of  Raspberry  and  Blackberry.    111.  Agl.  Exp. 

Sta.  Built.  29:   273-296.   pis.  1-4.    1893. 
FARLOW,  W.  G.    Notes  on  Some  Species  in  the  Third  and  Eleventh  Centuries 

of  Ellis's  North  American  Fungi.    Proc.  Amer.  Acad.  Arts  and  Sci.,  N.  S. 

18:  65-85(76).    1883. 
NEWCOMBE,  F.  C.    Perennial  Mycelium  of  the  Fungus  of  Blackberry  Rust. 

Journ.  Mycology  6 :    106-107.  pis.  5,  6.    1890. 
RICHARDS,  H.  M.    On  the  Development  of  the  Spermogonium  of  Caeoma 

nitens  (Schw.).    Proc.  Amer.  Acad.  Arts  and  Sci.,  N.  S.  20  :  30-36.  pi.  i. 

1893. 
TRANZSCHEL,  W.    Culturversuche  mit  Caeoma  interstitiale  Schlechtd.  (- C. 

nitens  Schw.).     Hedwigia  32  :   257-259.    1893. 

Occurrence  and  symptoms.  The  orange  rust  is  a  common  disease 
of  black  raspberries  and  blackberries  throughout  portions  of  the 
United  States  and  Canada,  and  it  is  also  widely  distributed  in 
Europe  and  Asia.  It  is  found  upon  various  species  of  the  genus 
Rubus,  whether  wild  or  cultivated,  although  there  is  considerable 
difference  in  the  susceptibility  of  different  varieties  of  the  same 
species.  Among  raspberries  Clinton  has  cited  the  Kittatinny  as 
perhaps  the  worst  affected,  and  the  Snyder  as  notably  resistant. 
In  other  regions,  however,  the  latter  has  proved  less  resistant. 
The  fungus  may  be  noted  almost  as  soon  as  the  young  leaves  be- 
gin to  appear  in  the  spring.  The  spermogonial  stage  appears  first 
and  gives  to  the  surface  of  leaves  and  even  young  stems  a  glandu- 
lar appearance,  which  may  often  be  mistaken  for  a  natural  condi- 
tion. A  comparison,  however,  of  affected  with  unaffected  plants 
readily  demonstrates  the  specific  effects  of  the  fungus.  At  times 
the  spermogonia  are,  however,  limited  in  distribution,  affecting  only 
a  portion  of  the  leaves  of  a  bud,  or  merely  small  areas  upon  a 
single  leaf.  In  from  ten  to  fifteen  days  after  the  appearance  of 
the  spermogonia  the  striking  aecidial  stage  may  be  found  appear- 
ing only  on  the  lower  surface  of  the  leaf.  The  cushions  which 
produce  the  spores  are  rapidly  developed  beneath  the  epidermis, 
and  upon  the  rupture  of  the  latter  the  bright  orange  spores  are 
disclosed.  Eventually  the  under  surfaces  of  the  leaves  may  ap- 
pear to  be  covered  with  a  continuous  mass  of  more  or  less  adhe- 
sive orange-red  material.  All  of  the  vegetative  parts  of  the  plant 
which  are  affected  are  usually  greatly  impaired  in  vitality  and 


428 


FUNGOUS  DISEASES  OF  PLANTS 


frequently  appear  spindling  from  the  beginning.  Nevertheless,  the 
affected  shoots  or  canes  may  not  be  killed,  and  the  disease  may 
reappear  upon  such  affected  plants  the  following  year  from  the 
growth  of  the  mycelium  into  young  shoots.  In  the  end,  practically 
all  affected  plants  are  killed,  and  their  vitality  is  from  the  outset 
so  diminished  that  productiveness  is  impossible. 


FIG.  208.    BLACKBERRY  RUST,  C^EOMA  STAGE 
To  the  left,  normal  shoots ;  to  the  right,  diseased 

The  fungus.  The  mycelium  of  this  fungus  has  been  carefully 
studied  in  the  growing  canes.  It  is  intercellular,  and  grows  rap- 
idly in  the  direction  of  formative  tissues,  or  where  new  cells  are 
being  produced,  extending  but  slightly  into  tissues  or  organs  which 
have  matured.  The  mycelium  is  richly  provided  with  haustoria. 
The  tip  of  the  haustorium  enlarges  as  a  knob-like  organ,  and  this 
is  commonly  more  or  less  in  contact  with  the  cell  nucleus.  The 
mycelium  in  the  root  penetrates  the  parenchymatic  cortical  cells, 


PROTOBASIDIOMYCETES 


429 


and  in  the  regions  where  the  hyphae  are  abundant  the  amount  of 
starch  is  distinctly  less  than  in  those  not  pervaded  by  the  fungus. 
In  the  stem,  according  to  Clinton,  the  mycelium  is  found  espe- 
cially in  the  pith,  in  a  more  or  less  zonal  area  situated  near  the 
fibro vascular  system.  The  young  mycelium  is  more  readily  seen 
on  account  of  the  greater  amount  *  of  coloring  matter  which  it 
contains. 

The  structure  of  the  spermogonial  stage  has  been  carefully  stud- 
ied  by  Richards.  His  work  indicates,  that  the  spermogonia  arise  as 
a  bundle  of  septate  threads  which  press  against  the  surrounding 


a  b 

FIG.  209.    C^EOMA  STAGE  OF  GYMNOCONIA  PECKIANA.  (After  Clinton) 
a,  general  effect  on  leaf ;  <5,  cross  section  through  a  young  sorus 

cells  so  as  to  cause  them  to  collapse,  and  these  injured  cells  are 
finally  penetrated  by  the  mycelium.  On  reaching  full  growth  small 
spore-like  bodies  are  abscised  from  the  ends  of  each  thread  ;  and 
when  produced  in  quantity,  the  epidermis  is  ruptured,  or  punctured, 
and  the  spores  ooze  out  as  a  small  glandular  droplet.  It  has  not 
been  shown  with  certainty  that  these  spores  have  been  germinated. 
The  observations  upon  a  budding  habit  suggested  by  early  ob- 
servers may  have  concerned  themselves  with  yeast  cells  asso- 
ciated with  the  spores  and  accidentally  introduced  into  the  culture 
drop. 


430  FUNGOUS  DISEASES  OF  PLANTS 

The  aecidial  or  caeomal  stage  may  cover  practically  the  whole  of 
the  lower  surfaces  of  the  leaves.  This  stage  is  the  one  of  great  im- 
portance from  the  standpoint  of  the  propagation  or  dissemination 
of  this  fungus.  In  the  formation  of  the  spores  extensive  mycelial 
cushions  are  developed  near  the  lower  surface  of  the  leaf,  and  from 
these  cushions  there  arise  cells  perpendicular  to  the  surface,  which 
elongate,  and  in  time  originate  chains  of  the  aecidiospores.  The 
development  of  these  spores  effects  a  rupture  of  the  epidermis,  so 
that  the  mature  spores  are  exposed  (Fig.  209).  The  maturity  of  the 
spore  involves  the  development  of  a  considerable  amount  of  color- 
ing matter  in  the  protoplasm,  so  that  when  the  spores  are  exposed, 
the  under  surface  of  the  leaf  is  bright  orange.  The  spores  are 
ordinarily  ovoidal  or  more  or  less  globose,  sharply  verrucose,  and 
measure  I2-24X  18-32/11.  Germination  may  take  place  immedi- 
ately, upon  maturity  of  the  spores,  and  the  Rubus  hosts  may  be 
promptly  infected.  The  lack  of  a  true  peridium  in  this  stage  is  the 
chief  reason  for  separating  the  species  generically  from  species  of 
Puccinia. 

The  teleutosporic  form  of  this  species  is  of  the  Puccinia  type. 
Prior  to  the  experiments  of  Tranzschel  and  Clinton,  working  inde- 
pendently, it  bore  the  name  Puccinia  Peckiana.  The  teleutosporic 
form  is  relatively  far  less  abundant  than  the  other  stages.  The  chief 
peculiarity  is  found  in  the  location  of  the  germ  pore  in  the  basal 
cell,  which  is  always  considerably  below  the  dividing  wall. 

XXIV.    RUST    OF    ROSES 
Phragmidium  subcortidum  (Schrank)  Wint. 

BANDI,  W.    Beitrage  zur  Biologic    der  Uredineen  (Teil  I).    Hedwigia    42  : 
118-136.    1903. 

The  various  species  of  Phragmidium  are  parasitic  upon  different 
rosaceous  hosts.  No  species  of  these  rusts  produces  any  very 
serious  disease  of  a  cultivated  variety ;  nevertheless,  consideration 
should  be  given  to  a  general  study  of  one  member  of  this  genus. 
The  fungus  above  indicated  occurs  commonly  in  moist  regions 
upon  several  wild  roses.  Spermogonia  and  aecidia  (caeoma  type) 
are  produced  on  the  stems,  petioles,  leaf  veins,  etc.,  as  orange- 
red  pustules,  sometimes  inclosed  by  paraphyses.  The  spores  are 


PROTOBASIDIOMYCETES 


431 


produced  in  short  chains  and  measure  24-28  x  18-21  //,  (Fig.  210, b). 
The  uredesori  occur  on  the  under  surface  of  the  leaf.  They  are 
somewhat  lighter  colored  than  the  caeoma  and  are  constantly 
inclosed  by  paraphyses.  Individual  spores  are  about  the  same  in 
size  and  form,  however,  as  the  previous  type  (Fig.  210,  c).  In  the 
same  sori  with  the  latter  may  be  produced  also  the  teleutospores, 


FIG.  210.  PHRAGMIDIUM  SUKCORTICIUM 
a  and  d,  caeoma  and  teleuto  stages  on  rose  ;  t>,  c;  and  c,  spore  forms 

usually  in  small  black  groups.  A  teleutospore  is  more  or  less 
spindle-shaped,  usually  six  to  eight  cells  in  extent  (Fig.  210,  e),  and 
each  cell  is  provided  with  several  germ  pores.  The  outer  wall  of 
the  spore  is  generally  uneven  or  warty  toward  the  apex,  and 
there  is  a  distinct  terminal  papilla.  The  teleutospores  measure 
65—100  x  30-45  ft  without  the  pedicel.  The  pedicel  is  persistent, 
swollen  at  the  base,  and  about  as  long  as  the  spore.  The  cells  of 
the  teleutospore  adhere  closely,  while  in  some  other  species  they 
separate  readily  on  maturity. 


432  FUNGOUS  DISEASES  OF  PLANTS 

XXV.    RUST  OF  RHODODENDRON  AND  NORWAY  SPRUCE 
Chrysomyxa  Rhododendri  (De  C.)  De  Bary 

Occurrence.  The  rhododendron  rust  is  especially  abundant  in 
portions  of  Europe  and  America,  particularly  in  regions  where  the 
wild  species  of  the  rhododendron  and  of  the  fir  grow  together  in 
the  same  forest  areas.  In  fact,  the  rust  is  the  most  common  fun- 
gus of  the  rhododendron,  and  in  regions  where  the  fir  abounds 
the  rhododendron  is  seldom  free  from  its  attacks.  In  Europe  it  is 
notably  abundant  on  Rhododendron  hirsutuwi  and  on  Rhododendron 
ferrugineum,  these  being  trfe  hosts  upon  which  the  uredo  and 
teleuto  stages  are  found.  The  spermogonial  and  ascidial  stages 
are  confined  to  the  fir  (Picea  excelsd).  In  the  United  States  this 
fungus  is  particularly  common  in  the  mountains  of  the  East,  and 
southward  as  far  as  the  southern  limits  of  the  Appalachians. 

The  spore  forms.  The  spherical  spermogonia  appear  upon 
young  leaves  of  the  fir  in  the  spring,  and  these  are  followed  a 
month  or  more  later,  sometimes  as  late  as  midsummer,  by  the 
aecidial  stage.  The  aecidia  break  through  the  epidermis  of  the 
leaf  as  more  or  less  tuberculate  structures  arising  thickly  on 
the  under  surfaces  of  the  leaves  to  a  height  of  two  or  three  milli- 
meters, each  producing  numerous  aecidiospores.  The  latter  germi- 
nate readily,  and  the  host  is  penetrated  by  means  of  the  stomata. 
It  is  claimed  that  the  mature  leaves  of  the  rhododendron  are  those 
generally  infected.  The  mycelium  developed  in  such  persistent,  or 
evergreen,  leaves  winters  over  and  produces  abundantly  the  uredo 
stage,  followed  also  by  the  teleutosporic  stage.  The  uredo  stage 
serves  to  spread  rapidly  the  fungus  from  one  plant  to  another 
during  the  growing  season.  The  teleutosporic  stage,  however,  ger- 
minates immediately,  and  the  basidiospores  penetrate  the  young 
shoots  of  the  fir,  thus  completing  the  life  cycle  of  this  euheterouredo. 
The  uredosporic  pustules  appear  only  on  the  under  surfaces  of  the 
leaves,  or  occasionally  on  the  younger  stems,  and  these  spores  are 
borne  in  chains  with  alternate  sterile  cells.  The  teleutospores  are 
closely  adherent  in  groups.  They  'are  more  or  less  cylindrical  in 
form,  extremely  light  in  color,  and  vary  as  to  the  number  of  cells 
from  three  to  six,  those  at  the  center  of  the  group  showing  the 
larger  number  of  cells. 


PROTOBASIDIOMYCETES  433 

Control.  No  attempts  have  been  made  to  control  this  disease, 
and  it  is  doubtful  if  any  effective  method  could  be  found,  except 
that  of  excluding  one  or  the  other  of  the  two  hosts  from  any 
particular  region.  It  is,  moreover,  possible  that  the  uredo  stage 
may  serve  to  transmit  the  disease  from  season  to  season  upon 
the  rhododendron. 

XXVI.    THE  EUROPEAN  CURRANT  RUST 
Cronartium  Ribicola  Fisch.  de  Waldh. 

HENNINGS,  P.  Beobachtungen  iiber  das  verschiedene  Auftreten  von  Cronar- 
tium ribicola  Dietr.  auf  verschiedenen  Ribes-Arten.  Zeitschr.  f .  Pflanzenkr. 
12:  129-132. 

KLEBAHN,  H.  Ueber  die  Formen  und  den  Wirthswechsel  der  Blasenroste 
der  Kiefern.  Ber.  d.  deut.  bot.  Ges.  8:  (59X70).  l89°- 

KLEBAHN,  H.  Neue  Untersuchungen  und  Beobachtungen  iiber  die  Blasen- 
roste der  Kiefern.  Hedwigia29;  27-35.  1890. 

PLOWRIGHT,  C.  B.  Fungus  on  Weymouth  Pine  and  on  Currants.  Card. 
Chron.  12(111):  44.  1892. 

STEWART,  F.  C.  An  Outbreak  of  the  European  Currant  Rust.  N.  Y.  Agl. 
Exp.  Sta.  Tech.  Built.  2:  62-74.  Pls-  1-3.  1906. 

v.  TUBEUF,  K.  Infektionsversuche  mit  Peridermium  Strobi,  dem  Blasenroste 
der  Weymouthskiefer.  Arbeiten  aus  der  Biolog.  Abt.  f.  Land-  u.  Forst- 
wirtschaft  am  Kaiserl.  Gesundheitsamte  2:  173-175.  1901.  (Abstract 
in  Centrbl.  Bakt.  u.  Parasit.  7  (Abt.  II):  445.) 

Occurrence.  Until  within  the  past  few  years  this  fungus  was 
known  to  be  of  importance  only  in  Europe,  and  indeed  as  yet 
only  sporadic  cases  have  been  found  in  other  parts  of  the  world. 
At  Geneva,  N.  Y.,  there  was  an  outbreak  on  currants  during  1906, 
and  special  measures  were  taken  to  stamp  out  the  fungus  in  that 
vicinity.  It  appears  also  that  the  fungus  is  known  in  India.  The 
aecidial  stage  of  this  fungus  was  named  Peridermium  Strobi,  by 
Klebahn,  but  inoculation  experiments  made  subsequently  both  by 
the  author  of  this  species  and  by  others  have  demonstrated  its  con- 
nection with  the  uredo  and  teleuto  forms  found  on  currants.  The 
aecidial  stage  has  been  reported  most  destructive  to  the  white  pine 
(Finns  strobus)  in  many  parts  of  Europe.  The  injuries  caused 
by  the  uredo  and  teleuto  stages  upon  the  currant  are,  however,  not 
of  sufficient  importance,  of  themselves,  to  arouse  particular  in- 
terest. In  this  connection  it  is  instructive  to  note  that  the  white 
pine  is  a  native  of  America ;  and  it  seems  remarkable,  when  the 
susceptibility  of  this  species  in  Europe  is  considered,  that  the 


434 


FUNGOUS  DISEASES  OF  PLANTS 


fungus  should  not  long  ago  have  appeared  in  America.1  The 
aecidial  stage  is  also  found  upon  another  species  of  pine,  Pinus 
cembra,  and  it  is  believed  by  some  that  the  fungus  is  indigenous 
upon  this  species  in  Russia  and  in  Switzerland. 

Host  plants.    The  uredo  and  teleuto   stages   (Fig.  211)  occur 
upon   many  varieties  of    the    genus    Ribes,    representing   several 


FIG.  211.    CRONARTIUM  RIBICOLA 

a,  sori  on  currant  leaf ;  l>,  sorus  and  teleutosporic  column  ;  c  and  d, 
uredospores  and  teleutospores 

1  During  June,  1909,  the  aecidial  stage  of  this  fungus  was  found  in  a  nursery 
of  three-year-old  white  pine  seedlings  imported  from  Germany.  Many  seedlings 
of  this  importation  have  been  distributed  to  several  northeastern  states  and  to 
Canada.  A  determined  effort  is  being  made  to  inspect  all  plantings,  to  destroy 
the  diseased  stock,  and  also  to  prevent  further  importation  of  the  infected  white 
pine  seedlings.  Inspection  of  such  seedlings  at  the  time  of  importation  is  prac- 
tically valueless,  since  the  fungus  has  an  incubation  period  in  the  bark  of  nearly 
one  year  before  the  characteristic  swellings  appear.  Details  of  the  outbreak  in 
New  York  are  discussed  in  the  following  articles : 
Atwood,  G.  G.  Blister  Rust  of  Pines  and  the  European  Currant  Rust.  Dept. 

Agl.,  State  of  N.  Y.    Hort.  Built.  2  :  1-15.    1969. 
Spaulding,  Perley.     European    Currant    Rust    on    the  White   Pine   in  America. 

Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Circular  38  :   1-4.    1909. 


PROTOBASIDIOMYCETES  435 

different  species.  According  to  Stewart  forty-eight  out  of  fifty-four 
varieties  of  currants  were  affected  in  one  plantation  in  the  Geneva 
outbreak,  representing  the  three  species  Ribes  nigrum,  Ribes  ru- 
brum,  and  Ribes  aureum.  The  only  varieties  which  were  free 
from  the  fungus  in  this  attack  were  the  following  :  Prince  Albert, 
Gondouin  White,  Stultz,  and  an  unknown  variety,  all  of  Ribes 
rubrum,  and  Crandall  and  Utah  Golden  of  Ribes  aureum.  In 
another  plantation  where  sixteen  different  species  of  Ribes  were 
cultivated,  only  one  species,  Ribes  irriguum,  was  rusted,  but  these 
plantations  did  not  include  Ribes  nigrum  and  Ribes  rubnim. 

Control.  In  attempting  to  control  or  stamp  out  this  disease,  it 
would  seem,  with  the  information  at  hand,  that  the  only  hope 
would  lie  in  the  destruction  of  one  or  the  other  of  the  two  hosts, 
the  currant  or  pine.  It  is  assumed  in  this  connection  that  the 
two  host  plants  are  invariably  essential  to  the  maintenance  of  the 
fungus.  Since  the  fungus  appears  to  be  of  little  importance  as  a 
disease  of  currants,  the  growers  of  this  fruit  evidently  will  not  re- 
sort to  heroic  measures,  and  it  will  devolve  upon  foresters  to  watch 
closely  for  the  fungus,  and  if  it  appears,  eliminate  the  wild  species 
of  Ribes  from  the  forest  area. 

XXVII.    ORANGE  RUST  OF  ASTER  AND  GOLDEN-ROD 

Coleosporium  Solidaginis  (Schw.)  Thiim. 

ARTHUR,  J.  C.,  and  KERN,  F.  D.    North  American  Species  of  Peridermium. 

Built.  Torrey  Bot.  Club  33:  403-438.    1906. 
CLINTON,  G.  P.    Peridermium  acicolnm,  the  ^Ecial  Stage  of  Coleosporium 

Solidaginis.    Science  25 :   289-290.    1907. 
CLINTON,  G.  P.    Hetercecious  Rusts  of  Connecticut  having  a  Peridermium 

for  their  ^cial  Stage.    Conn.  Agl.    Exp.    Sta.  Rept.   (1907):    369~396- 

pis.  25-32. 

Occurrence.  Of  the  several  species  of  Coleosporium  having 
uredospores  and  teleutospores  on  species  of  Composite,  there  is 
none  of  such  common  occurrence  throughout  North  America  as 
the  species  here  discussed.  To  this  species  are  referred  the  orange 
rusts  of  many  species  of  Aster  and  Solidago  (golden-rod).  It  in- 
cludes also  as  hosts  representatives  of  several  other  genera,  among 
which  is  the  cultivated  aster  (Callistephus  hortensis).  This  fungus 
is  by  many  regarded  as  identical  with  a  species  occurring  wide- 
spread in  Europe  upon  Senecio, 


436 


FUNGOUS  DISEASES  OF  PLANTS 


The  genus  Coleosporium  is  to  be  considered  entirely  heterce- 
cious,  and  whenever  aecidial  stages  are  known  in  the  life  cycle, 
they  occur  on  species  of  Pinus,  and  are  referable  to  the  form 
genus  Peridermium. 

The  aecidial  stage  of  the  species  here  discussed  has  recently 
been  found  through  inoculation  experiments  to  be  a  form  known 

a s  Pe ride rmiu m 
acicolum  occurring 
on  leaves  of  Pinus 
rigida  in  several 
of  the  northeastern 
states.  The  Euro- 
pean form  occurs 
upon  branches  and 
stems  of  Pinus 
sylvestris. 

The  fungus.  The 
uredo  and  teleuto 
stages  are  merely 
conspicuous  by 
their  color,  and  in 
this  particular  in- 
stance the  aecidial 
stage  is  by  no 
means  striking. 
Other  forms  or 
species  of  Peri- 
dermium, however, 
may  produce  considerable  swellings  upon  their  hosts. 

According  to  Clinton  the  infection  of  young  pine  leaves  may 
take  place  in  spring,  the  aecidia  resulting  the  following  year.  It 
would  appear  that  the  Peridermium  is  inessential  for  the  continu- 
ous propagation  of  the  rust  upon  composites  in  the  United  States, 
since  the  uredo  stage  is  produced  practically  throughout  the  winter 
on  leaves  of  the  basal  rosettes. 

The  spermogonia  appear  upon  the  needles  in  autumn,  but  the 
aecidia  are  not  developed  until  spring.  They  occur  on  both  sur- 
faces of  the  leaves  in  slightly  discolored  spots,  They  are  crumpent, 


FIG.  212.   PERIDERMIUM  ON  PINE.  (After  Hartig) 


PROTOBASIDIOMYCETES 


437 


tongue-shaped  bodies  .5-.7.mm.  high,  opening  by  an  irregular  rup- 
ture of  the  peridium.    The  spores  are,  according  to  Arthur,  coarsely 

verrucose  with  deciduous  tuber- 
cles, except  along  one  narrow 
line,  where  tubercles  fail. 

The  uredospores  are  produced 
in  orange-yellow  sori,  which  soon 
fade  to  nearly  white.  They  are 
generally  ellipsoidal,  measuring 
27-30  x  1 7-22  p.  The  teleuto- 
spores  are  borne  in  crowded 
waxy  masses,  and  are  at  maturity 
a  chain  of  four  basidial  cells  within 
a  somewhat  gelatinized  common 
wall.  They  are  sessile,  5  5-80  x 
I5-23//,,  and  the  cell  wall  at  the 
apex  is  generally  swollen,  often 
FIG.  213.  COLEOSPORWM  SEXECIONIS  attaining  a  maximum  thickness 

(b  after  Tulasne)  of  3O— 4O//.. 


XXVIII.    RUST    OF    POPLAR 
Melampsora  tremulcz  Tul. 

Tulasne  applied  the  above  name  to  a  rust  of  the  poplar  (Popuhis 
tremuld]  occurring  throughout  a  considerable  range  in    Europe. 
It  would  seem     . 
that  this  name 
would  now   in- 
clude at  least 
three  forms,  or 
species,  as  dis- 
tinguished  by 
Klebahn,   viz., 
Melampsora  Pinitorqua 
Rostr.,   Melampsora 
Larici-tremulce    Kleb., 
and  Melampsora  Mag-    FIG.  214.  MELAMPSORA  TREMVLA*:  UREDOSPORES 
nusiana  Wagn.    These  AND  TELEUTOSPORES 


438  FUNGOUS  DISEASES  OF  PLANTS 

three  forms,  together  with  one  discussed  by  Klebahn  as  Melanip- 
sora  Rostrupii  Wagn.,  all  agree  in  having  more  or  less  spherical 
uredospores,  and  in  no  case  are  there  marked  morphological  dif- 
ferences in  the  uredospores  or  teleutospores  within  this  group.  The 
caeoma  stages  have,  however,  been  determined,  for  these  forms,  to 
occur  respectively  upon  Pinus,  Larix,  Chelidonium  and  Corydalis, 
and  Mercurialis.  For  our  purpose,  it  does  not  matter  particularly 
whether  these  forms  are  considered  a  group  of  closely  related 
species,  or  merely  well-established  physiological  forms  of  a  single 
variable  species.  In  Europe  these  are  found  chiefly  upon  Populus 
tremula  and  Populus  alba.  In  the  United  States  it  would  seem 
difficult  at  the  present  time  to  name  the  hosts  positively,  although 
Populus  tremuloides  may  be  specially  mentioned. 


CHAPTER  XV 

AUTOBASIDIOMYCETES 

In  this  class  the  sporophore  or  mycelial  body  may  be  of  most 
diverse  form.  The  most  essential  character,  however,  is  that  ordi- 
narily a  portion  of  the  sporophore  is  eventually  differentiated  into 
a  close  layer,  the  hymenium,  from  which  arise,  in  a  palisade  man- 
ner, clavate  or  cylindrical  basidia.  Each  basidium  produces  four 
(occasionally  two,  six,  or  eight)  unicellular  basidiospores,  each  on 
a  relatively  short  sterigmatum.  The  fruit  body,  or  sporophore,  may 
reach,  in  this  class,  the  maximum  size  and  complexity  attained 
among  fungi. 

I.    EXOBASIDIALES  (EXOBASIDIACEyE) 

BREFELD,  O.    Die  Gattung  Exobasidium.   Unters.  a.  d.  Gesamtgeb.  d.  Myk., 

8:    12-18.    1889. 
GEYLER,  H.  TH.    Exobasidium  Lauri,  nov.  sp.    Bot.  Zeit.  32  :  321-326.  pi.  6. 

1874. 
WORONIN,  M.    Ueber  die  Sclerotienkrankheit  der  Vaccinienbeeren.    Me"m. 

acad.  imp,  de  St.-Petersbourg  36  (Ser.  7):   28-30.    1888. 

The  members  of  this  order  are  distinguished  from  other  Basid- 
iomycetes  chiefly  in  two  characteristics,  first,  that  the  mycelium  is 
strictly  parasitic,  producing  generally  a  gall-like  hypertrophy  made 
up  of  mycelium  and  host  tissue  ;  and  second,  that  there  is  produced 
no  definite  sporophore ;  instead,  the  basidia  break  through  the  epi- 
dermis of  the  host. 

Four  sporidia  are  commonly  produced  (occasionally  five  or  six). 
The  spores  are  curved,  and  germinate  in  nutrient  media,  so  far  as 
known,  after  one  or  more  cross  partitions  are  formed.  Germina- 
tion is  then  more  or  less  equivalent  to  a  budding  process,  in  which 
numerous  spindle-shaped  cells  are  produced. 

The  genus  Exobasidium  is  most  important,  and  the  majority  of 
the  species  produce  deformities  upon  different  genera  of  heaths 
(Ericaceae). 

439 


440 


FUNGOUS  DISEASES  OF  PLANTS 


II.    GALL  OF  HEATHS 
Exobasidium  Vaccinii  (Fckl.)  Wor. 

RICHARDS,  H.  M.  Notes  on  Cultures  of  Exobasidium  Andromedae  and  of 
Exobasidium  Vaccinii.  Botan.  Gaz.  21 :  101-108.  pi.  6.  1896. 

SHEAR,  C.  L.  Cranberry  Diseases.  Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built. 
110:  35-37-  pi-  7-  i9°7- 

Relationship  of  forms.  Much  cross-inoculation  work  is  needed 
to  determine  the  relationship  between  forms  of  Exobasidium  on 
different  species  of  heath  (Ericaceae).  These  fungi  are  found 

upon  certain  more  or  less 
closely  related  hosts,  generally 
in  bog-like  habitats  throughout 
considerable  portions  of  Europe 
and  North  America. 

The  fungus  upon  Vaccinium 
Vitis-idaa  is  considered  the 
typical  form  of  the  species 
here  discussed.  Upon  the  host 
referred  to,  pale  rose  or  red- 
dish, thickened  spots  are  pro- 
duced. The  same  species 
occurs,  apparently,  on  other 
species  of  Vaccinium,  also 
Gaylussacia  and  other  genera, 
and  it  may  be  well  briefly 
to  refer  to  some  of  its  related  forms.  No  morphological  char- 
acters of  the  fungus  above  mentioned  have  been  found  which 
would  distinguish  it  from  Exobasidium  Oxycocci  Rostr.  on  the 
cranberry  (Vaccinium  macrocarpon).  On  the  cranberry,  however, 
lateral  buds  are  attacked,  and  as  these  exfoliate,  a  considerable 
portion  of  the  shoot  may  become  hypertrophied.  The  affected 
leaves  are  rose  colored,  and  since  they  remain  close  together  on 
the  shoot,  they  are  often  called  false  blossoms.  A  form  produc- 
ing characteristic  galls  on  the  young  shoots  of  several  species  of 
rhododendron  is  generally  regarded  as  distinct,  and  bears  the 
name  Exobasidium  Azalea.  Finally,  there  is  an  unusually  large 
form  described  as  Exobasidium  Andromeda  Pk.,  which  produces 


FIG.  215.   EXOBASIDIUM  VACCINII  ON 
RHODODENDRON 


AUTOBASIDIOMYCETES 


441 


distortions  on  young  shoots  of  Andromeda  ligustrina.  Galls  of 
this  latter  form  are  hollow,  bag-like  structures  which  may  attain  a 
length  of  five  or  six  inches. 

Richards  employed  the  large  form  on  Andromeda  and  Exo- 
basidium  Vaccinii  in  some  cross  inoculations  and  was  able  to 
develop  the  leaf  spot  form  of  the  gall  on  Andromeda  from  Exo- 
basidium  Vaccinii,  and  also  to  produce  this  same  form  through 
spores  from  the  galls  on  Andromeda.  He  also  directs  attention 
to  the  fact  that  the  larger  distortions  in 
general  are  produced  only  during  the 
early  part  of  the  year,  that  is,  when  the 
fungus  attacks  the  young  and  sensitive 
tissue.  Cross-inoculation  work  is  at- 
tended with  some  difficulty  on  account 
of  the  diversity  in  season  of  the  vari- 
ous forms,  and  probably  also  differ- 
ences in  the  susceptibility  of  the  hosts 
as  the  season  advances. 

The  fungus.  The  hyphae  are  fine, 
much  branched,  and  commonly  inter- 
cellular. They  are  most  abundant  in 
the  subepidermal  layers,  and  in  the  case 
of  the  forms  producing  galls  upon  the 
young  stems  they  are  more  or  less  con- 
fined to  the  cortical  parenchyma.  The 
basidia  arise  directly  from  the  hyphae, 
pushing  up  between  the  epidermal  cells.  A  basidium  bears  fre- 
quently four  spores,  but  two  to  seven  may  be  produced.  The  spores 
are  elliptical  or  slightly  curved  and  ordinarily  measure  14-17  X  3//<. 
Among  the  basidia,  at  intervals,  may  appear  certain  branched 
conidiophores  bearing  small  acicular  conidia.  This  is  apparently 
the  chief  conidial  type  in  the  genus  Exobasidium. 


FIG.  216.  EXOBASIDIUM  VACCINII 
(After  Woronin) 


III.    HYMENOMYCETALES 


Among  the  higher  Basidiomycetes  the  important  forms  from 
the  view  point  of  the  economic  plant  pathologist  are  included  in 
a  few  families  of  the  Hymenomycetales.  This  order  includes  the 


442 


FUNGOUS  DISEASES  OF  PLANTS 


great  majority  of  the  plants  commonly  known  as  mushrooms,  toad- 
stools, punks,  etc.,  plants  exceedingly  variable  in  size,  form,  and 
texture.  The  mycelium  is  generally  abundant,  and  it  is  made  up 
of  relatively  minute  hyphse  in  loose  wefts  or  flocculent  masses, 
sometimes  closely  united  into  bands  or  strands  (rhizomorphs),  and 
often  perennial.  Sclerotia  also  occur.  The  fruit  body  varies  from 
what  is  merely  a  close  hyphal  weft  to  bodies  most  diversely  consti- 
tuted, and  very  complex  in  structure  (sporophores).  In  fact,  the  fruit 
body  may  be  felt-like,  pellicular,  leathery,  fleshy,  corky,  or  woody 
in  texture.  Conidial  stages  of  several  types  are  present  in  some 
families,  but  in  this  group  these  imperfect  forms  have  not  the  same 
relative  significance  in  propagation  as  in  the  Ascomycetes.  The 
mycelium  of  a  majority  of  the  parasitic  or  wood-destroying  species 
may  be  grown  in  artificial  cultures  in  the  laboratory.  Frequently 
the  best  growth  is  obtained  when  such  materials  as  dead  wood, 
decayed  leaves,  and  rich  soil  are  substituted  for  the  usual  media. 

The  families  and  genera  here  to  be  considered  consist  of  solid 
sporophores,  briefly  characterized  as  follows  : 

1 .  Thelephoracece.   The  hy menial  surface  is  more  or  less  smooth. 
Sporophores  are  skin-like,  gelatinous,  or  woody  in  texture,  spread 
out  over   the   surface  of   the  substratum    (resupinate),   shelving, 
stalked,  or  considerably   branched.    Corticium  and  Stereum  are 
important  genera. 

2.  Hydnacece.    The  hymenial    surface   is  usually  spread   over 
tooth-like  divisions  of  the  sporophore,  the  latter,  however,  some- 
times wart-like  or  even  more  or  less  briefly  plate-like  (lamelliform). 
The  sporophores  are  very  diversely  formed.    The  genus  Hydnum 
alone  will  be  considered. 

3.  Polyporacecz.    The  hymenial  surface  is  generally  spread  over 
the  inner  surfaces  of  pores  or  narrow  tubes,  sometimes,  however, 
over  folds  or  shallow  depressions   between  vein-like   reticulations, 
occasionally  more  or  less  lamelloid.    The  sporophores  are  diverse, 
generally  tough,  often  very  large.    Those  most  important  in  the 
production  of  tree  diseases  are  typical  pore-bearing  species,  which 
may  be  assigned  to  one  of  three  closely  related  genera,  —  Fomes, 
Polyporus,  and  Trametes. 

4.  Agaricacecz.    The   hymenial  surface    is    confined    to   radial 
plates  or  lamellae,  the  latter,  however,  sometimes  in  the  form  of 


AUTOBASIDIOMYCETES  443 

folds  or  veins.  The  sporophores  are  generally  fleshy,  with  a  defi- 
nite cap,  or  pileus,  usually  provided  with  a  central  stalk,  but  also 
excentric,  sessile,  etc.  Marasmius,  Clitocybe,  and  Armillaria  are 
some  of  the  principal  parasitic  genera. 

Corticium,  including  resupinate  species  without  setae  (cystidia) 
on  the  hymenium.  The  spores  are  generally  small,  hyaline,  and 
without  appendages. 

Stereum  is  a  diverse  genus  with  broader  characteristics.  The 
sporophores  are  differentiated  into  several  layers.  They  are  only 
partially  if  at  all  resupinate,  and  often  shelving,  or  even  slightly 
stalked. 

Hydnum.  The  sporophores  are  provided  with  awl-like  teeth 
arising  from  tuberculate,  branched,  or  cap-like  portions  of  the 
sporophore.  No  cystidia  are  present. 

Fomes,  with  sporophores  generally  bracket-like  or  hoof-shaped, 
sessile  or  stalked,  and  woody  even  when  young.  The  pores  are 
narrow,  and  the  tissue  between  these  is  heterogeneous  with  the 
general  tissue  of  the  sporophore. 

Polyporus  is  similar  to  the  preceding,  except  that  the  sporophore 
is  at  first  fleshy,  becoming  harder,  and  it  may  be  exceedingly  diverse 
in  form  and  size. 

Trametes.  In  this  genus  the  species  are  generally  of  the  texture 
of  Fomes  or  Polyporus  ;  but  the  general  tissue  of  the  sporophore 
penetrates  between  the  pores,  so  that  there  is  homogeneity  of 
substance. 

Marasmius  is  a  genus  of  the  relatively  small  gill-bearing  fungi 
in  which  the  plants  become  dry,  yet,  when  remoistened,  regain 
much  their  original  forms.  The  cap  is  fleshy  to  leathery,  the  gills 
tough  and  distant,  producing  white  spores, ,  and  the  stipe  cartilagi- 
nous or  horny. 

Clitocybe,  with  more  or  less  fleshy  cap  and  stalk,  the  latter 
centrally  placed,  is  characterized  by  decurrent  gills  (lamellae)  and 
by  the  absence  of  any  appendages,  such  as  veil  or  volva.  The 
spore  powder  is  white  and  the  spores  hyaline. 

Armillaria.  These  forms  are  quite  similar  to  the  preceding  ex- 
cept that  when  young  the  cap  is  attached  to  the  stem  by  a  veil, 
which  upon  breaking  forms  a  more  or  less  persistent  ring  (annulus) 
on  the  stem. 


444  FUNGOUS  DISEASES  OF  PLANTS 

IV.    A  ROOT  AND  STEM  ROT  FUNGUS 
Cortidum  vagum  B.  &  C.,  var.  Solani  Burt. 

ATKINSON,  GEO.  F.    Some  Diseases  of  Cotton.    Ala.  Agl.  Exp.  Sta.  Built.  41 : 

30-39.    1892. 
CLINTON,  G.  P.    Rhizoctonia  (Rosette).    Conn.  Agl.  Exp.  Sta.  Rept.  (1904): 

325-326.  pi.  26.  figs.  a-c. 
DUGGAR,  B.  M.,  and   STEWART,  F.  C.    The   Sterile  Fungus  Rhizoctonia. 

Cornell  University  Agl.  Exp.  Sta.  Built.  186:   50-76.  figs.  15-23.    1901. 

Ibid.  N.  Y.  (Geneva)  Agl.  Exp.  Sta.  Built.  186  :  4-30.  figs.  15-23.    1901. 
PAMMEL,  L.  H.    Preliminary  Notes  on  a  Root-Rot  Disease  of  Sugar  Beets. 

Iowa  Agl.  Exp.  Sta.  Built.  15:   243-251.  pis.  3-4.    1891. 
ROLFS,  F.  M.    Potato  Failures.    (Two  Reports.)   Colo.  Agl.  Exp.  Sta.  Bulks. 

70:    1-20.    1902;  91:    1-33.    1904. 
ROLFS,  F.  M.    (Tomato  Diseases)  Cortidum  vagum  (B.  &  C.).    Fla.  Agl.  Exp. 

Sta.  Rept.  (1905):  46-47. 
SORAUER,  P.    Pflanzenkrankheiten  (2d  ed.),  /.  c.,  354-361. 

A  fungus  causing  important  diseases  of  the  potato  and  perhaps 
of  a  large  number  of  other  herbaceous  and  even  woody  plants  has 
recently  been  placed  under  the  name  above  given.  The  various 


ifr9&3$*% 

^gj$ 

*  ^jJv^  S 


FIG.  217.    LETTUCE  SEEDLINGS  ATTACKED  BY  RHIZOCTONIA 

plant  diseases  due  to  this  fungus  had  formerly  been  referred  to 
the  form  genus  Rhizoctonia,  which  is  a  genus  established  by 
De  Candolle  in  1815,  including  certain  sterile  fungi  occurring 
upon  the  roots  of  plants.  There  are  great  difficulties  in  determin- 
ing what  might  be  considered  species  in  forms  which  are  re- 
ferred to  this  form  genus,  and  the  Corticium  stage  has  not  yet 


AUTOBASIDIOMYCETES  445 

been  studied  in  sufficient  detail  to  be  of  much  assistance.  Never- 
theless, there  are  certain  characters  of  the  mycelium  by  means  of 
which  it  was  believed  to  be  possible  more  or  less  accurately  to 
distinguish  the  Rhizoctonia  from  the  mycelium  of  other  fungi,  or 
even  with  some  accuracy  to  distinguish  different  species  of  Rhi- 
zoctonia, or  sterile  stages  referred  to  the  genus.  It  is  only  within 
the  past  four  years  that  there  has  been  found  associated  with  the 
sterile  mycelial  form  (the  Rhizoctonia)  this  perfect  stage,  which 
has  been  determined  as  above  given.  It  would  seem  probable, 
however,  that  we  may  look  upon  some  of  the  rather  diverse  forms 
of  Rhizoctonia  as  truly  sterile  stages  of  the  Corticium  mentioned. 

Historical.  In  Europe  the  genus  Rhizoctonia  received  con- 
siderable attention  by  the  early  mycologists,  and  various  forms 
were  described  at  some  length  by  the  Tulasnes  (1851)  and  by 
Kiihn  (1858).  Moreover,  all  the  general  texts  on  plant  diseases 
have  given  some  consideration  to  these  forms.  In  the  United 
States  the  Corticium  vagum  of  Berkeley  and  Curtis  was  un- 
known, apparently,  prior  to  1904  as  the  cause  of  plant  diseases, 
yet  the  fungus  had  been  described  as  No.  262  of  the  North 
American  fungi,  occurring  upon  the  bark  of  pine  in  South 
Carolina.  In  1891  Pammel,  in  some  notes  on  beet  diseases, 
described  a  beet  root  rot,  which  he  believed  to  be  due  to  Rhi- 
zoctonia Betce  Kiihn.  From  the  mycelial  characters  of  the  fun- 
gus this  was  unquestionably  a  Rhizoctonia.  Further,  in  1892  a 
sterile  fungus  as  a  cause  of  damping-off  in  cotton  was  reported 
from  Alabama  (Atkinson),  and  later  the  same  author  described 
damping-off  of  various  seedlings  by  a  similar  unnamed  fungus  at 
Ithaca,  N.Y.  Since  1898  the  various  plant  diseases  due  to  this 
fungus  have  received  considerable  attention  in  this  country. 
Work  at  the  Cornell  and  New  York  (Duggar  and  Stewart),  Ohio 
(Selby),  Colorado  (F.  M.  Rolfs),  Florida  (F.  M.  Rolfs),  and  other 
experiment  stations  has  demonstrated  that  the  various  forms  of 
this  fungus  are  extremely  important  as  the  cause  of  various  types 
of  plant  diseases  in  this  country. 

Distribution  and  diversity  of  forms.  The  Rhizoctonia  is  un- 
questionably widely  distributed  in  the  United  States  and  in  Europe 
and  Asia.  In  fact,  wherever  a  careful  study  of  plant  diseases  has, 
been  made,  one  or  more  forms  of  this  fungus  have  been  found^ 


446 


FUNGOUS  DISEASES  OF  PLANTS 


and  it  is  very  probable  that  some  of  the  damping-off  which  has 
been  ascribed  to  Pythium  could  be  properly  referred  to  damage  by 
this  fungus.  It  is  not  possible  at  the  present  time  to  say  definitely 
that  such  damping-off  diseases  as  those  of  cotton,  lettuce,  etc.,  are 
produced  by  the  same  species  or  race  of  Rhizoctonia  as  that  which 

is  found  upon  the  potato,  but 
there  is  reason  to  believe  that 
the  differences  which  occur 
between  the  various  forms  of 
the  parasite  upon  a  large  num- 
ber of  hosts  are  only  such  as 
might  be  considered  varietal  or 
racial,  and  in  some  instances 
we  have  unquestionably  to  do 
with  physiological  forms.  It  is 
certain,  however,  that  Rhizoc- 
tonia Medicaginis  De  C.  of 
Europe  is  a  fungus  very  differ- 
ent from  the  common  potato 
fungus  of  Europe  and  America 
and  also  from  the  common 
species  producing  damping-off 
of  seedlings,  rot  of  beets,  etc., 
in  this  country.  Moreover,  a 
form  which  has  been  described 
(Duggar  and  Stewart)  on  rhu- 
barb is  likewise  a  very  different 
organism.  It  would  not,  how- 
ever, be  surprising  to  find  that 
a  very  large  number  of  the 
other  forms  which  have  been 
discussed  by  various  authors  may  be  ascribed  to  one  and  the  same 
species,  the  perfect  stage  of  which  would  now  appear  to  be  Corti- 
cium  vagum  B.  &  C.  var.  Solani  Burt. 

Effects  upon  the  hosts.  The  fungus  is  perhaps  most  disastrous 
as  a  damping-off  disease.  The  progress  of  the  disease  upon  seed- 
lings resembles  very  closely  that  of  Pythium,  and  it  is  affected  by 
similar  conditions.  The  plants  that  have  thus  far  seemed  to  be 


FIG.  218.    RHIZOCTONIA  ON  RADISH 
(Photograph  by  H.  H.  Whetzel) 


AUTOBASIDIOMYCETES 


447 


most  susceptible  are  such  as  lettuce  (Fig.  2 1 7),  sugar  beet,  celery, 
cotton,  and  the  seedlings  of  various  delicate,  ornamental  plants. 

Upon  the  potato  the  fungus  has  been  known  for  more  than 
half  a  century  in  Europe,  but  largely  through  the  presence  of  a 
sclerotial  stage  upon  the  tubers.  This  typical  sclerotial  stage 


m 


FIG.  219.    RHIZOCTONIA  ON  POTATO:  EUROPEAN  (UPPER)  AND 
AMERICAN  (LOWER)  SPECIMENS 

has  also  been  found  abundantly  in  the  United  States  during  the 
past  eight  years,  and  it  is  unquestionably  the  same  as  the  European 
form  (Fig.  219).  In  this  country,  however,  the  Rhizoctonia  was 
first  found  upon  the  stems  of  dying  potato  plants,  and  while  it 
does  not  seem  to  be  a  very  serious  disease  of  potatoes,  it  is  one 


448 


FUNGOUS   DISEASES   OF  PLANTS 


of  some  consequence.  It  is  perhaps  not  responsible  for  all  the 
injuries  which  have  been  ascribed  to  it  in  Colorado,  particularly 
in  so  far  as  the  production  of  the  disease  known  as  "  little  potato" 


FIG.  220.   RHIZOCTONIA  PRODUCING  A  CROWN  ROT  OF  BEETS 

is  concerned.  The  fungus,  however,  attacks  the  subterranean  parts 
of  the  stem,  as  well  as  penetrating  the  roots,  and  the  hyphae  are 
found,  for  the  most  part,  enveloping  stem  and  root,  or  distributed 


AUTOBASIDIOMYCETES  449 

within  the  pith.  The  sclerotia,  which  are  formed  upon  the  surface 
of  the  potatoes,  do  not  seem  to  produce,  in  any  case,  rotting  of  the 
tissues  below.  They  are  closely  adherent,  but  merely  superficial,  and 
perhaps  serve  particularly  for  the  distribution  of  the  fungus. 

Upon  the  sugar  beet  this  fungus  produces,  besides  the  damping- 
off  already  referred  to,  a  characteristic  form  of  rot.  The  leaves  are 
affected  at  the  bases,  and  these  pr.omptly  wilt  and  decay.  The  fun- 
gus gains  strength  and  penetrates  into  the  superficial  layers  of  the 
beet  root,  and  frequently  causes  serious  rotting,  accompanied  by 
cracking,  as  shown  in  Fig.  220. 

In  Europe  Rhizoctonia  Medicaginis  has  been  found  upon  the 
beet,  but  that  is  a  fungus  very  different  from  the  Corticium,  as 
subsequently  mentioned.  Moreover,  Rhizoctonia  Medicaginis  has 
not  been  found  in  this  country,  although  its  hosts  are  such  com- 
mon plants  as  the  asparagus,  alfalfa,  and  sugar  beet.  Some  of  the 
various  hosts  upon  which  the  forms  of  the  Rhizoctonia  allied  to 
Corticium  vagum  var.  Solani  have  thus  far  been  found  in  America 
are  as  follows  : 

Sugar  beet,  Beta  vulgaris, 

Bean,  Phaseolus  vulgaris, 

Carrot,  Daucus  Carota, 

Cabbage  and  Cauliflower,  Brassica  oleracea, 

Cotton,  Gossypium  hirsutum, 

Lettuce,  Lactuca  sativa, 

Potato,  Solatium  tuberosum, 

Radish,  Raphanus  sativus, 

Sweet  potato,  Ipomcea  Batatas, 

Pumpkin,  Cucurbita  Pepo, 

Watermelon,  Citrullus  vulgaris, 

Garden  pea,  Pisum  sativmn,  etc., 

as  well  as  upon  many  species  of  ornamental  plants  and  weeds. 

Upon  the  tomato  plant  this  fungus  attacks  also  the  subterranean 
/parts  of  the  stem  and  may  be  of  importance  where  the  soil  is  poorly 
aerated.  It  may  also  occur  upon  the  fruits  when  these  are  in  con- 
tact with  the  soil,  but  it  is  not  probable  that  it  becomes  a  fruit 
disease  except  when  fruit  has  been  previously  injured  in  some 
manner.  Upon  either  the  potato  or  the  tomato  the  fruiting  stage 
may  develop  upon  the  stems  above  the  surface  of  the  ground  to 
a  distance  of  several  inches. 


450 


FUNGOUS  DISEASES  OF  PLANTS 


Characters  of  the  fungus.  The  mycelium  varies  considerably 
in  form,  depending  upon  age,  or  the  conditions  under  which  grown. 
In  diseased  tissues  where  there  is  abundance  of  water,  or  in 
pure  culture,  the  young  hyphae  develop  branches,  which  are  usually 
inclined  at  an  acute  angle  to  the  direction  of  growth  of  the 

parent  branch,  although  subse- 
quently the  two  may  grow  par- 
allel. The  branch  is  usually 
somewhat  narrowed  or  con- 
stricted where  united  with  the 
main  hypha,  and  a  septum  is 
formed  at  a  distance  of  several 
micromillimeters  from  the 
point  of  origin  of  the  branch. 
The  hyphae  may  be  almost 
hyaline  when  young,  but  very 
generally  become  yellowish 
brown  with  age.  Furthermore, 
in  age  the  branches  appear  to 
be  more  at  right  angles,  at 
least,  so  far  as  the  origin  is 
concerned.  Upon  many  host 
plants,  and  especially  when  the 
fungus  is  grown  in  pure  cul- 
tures, a  short  tufted  growth  of 
the  mycelium  may  occur.  The 
hyphae  of  these  tufts  are  brown, 
closely  septate,  constricted  at 
the  septa,  and  often  branched 
in  an  irregular  dichotomous 
fashion  (Fig.  222,  b).  In  the 
latter  case  the  hyphae  readily 

break  up  into  short  hyphal  lengths,  consisting  of  a  single  cell  or 
more,  and  these  cells  are  able  to  germinate  within  a  few  hours 
when  placed  in  fresh  nutrient  media.  Germination  is  commonly 
by  means  of  a  germ  tube  protruded  from  a  septum.  A  germ  tube 
may  even,  in  some  cases,  pass  through  a  neighboring  cell.  It  would 
appear  that  the  fruiting  stage  usually  develops  upon  living  plants. 


FIG.  221.    RHIZOCTONIA  ON  BEAN 

STEMS  AND  PODS.    (Photograph  by 

M.  J.  Barrus) 


AUTOBASIDIOMYCETES 


451 


In  the  case  of  the  potato,  it  forms  a  membranous  layer  inclos- 
ing the  stem  for  several  inches  above  the  surface  of  the  ground. 
This  layer  is  composed  of  rather  loosely  interwoven  hyphae,  and 
on  account  of  this  character  it  is  difficult  to  say  if  the  plant  is 
properly  placed  under  the  genus  Corticium,  or  whether  it  might 
not  with  equal  propriety  be  considered  a  species  of  Hypochnus. 
The  basidia  are  short,  cylindrical,  or  oblong,  and  apparently  many 


FIG.  222.    CORTICIUM  I/AGUM  VAR.  SOLANI 
«,  young  hyphae  ;  l>,  cells  from  growth  in  tufts  ;  c,  basidia  and  spores 

may  be  produced  from  a  single  parent  hypha,  each  basidium  being 
cut  off  from  the  hypha  by  a  septum  placed  in  the  manner  charac- 
teristic of  the  branching  mycelium.  The  basidia  bear  four  sterig- 
mata  and  spores,  although  commonly  only  two  may  be  observed 
at  one  time.  The  spores,  according  to  Rolfs,  are  somewhat  ellip- 
tical or  irregular  in  outline,  frequently  obovate  and  nearly  hyaline, 
9-1 5  X  6-1 3 /z.  Spore  germination  proceeds  in  ordinary  nutri- 
ent media,  and  as  a  rule  a  septum  is  formed  in  the  germ  tube 
shortly  after  it  emerges  from  the  spore,  the  proximal  portion  of 
the  germ  tube  being  somewhat  less  in  diameter.  When  produced 


452  FUNGOUS  DISEASES  OF  PLANTS 

upon  the  majority  of  hosts  the  Corticium  stage  disappears  by  the 
time  the  host  plant  is  dead. 

A  considerable  amount  of  study  is  demanded  in  order  that  it  may 
be  determined  what  may  properly  be  considered  species  or  varieties 
within  this  group  of  plants.  Cross-inoculation  work  is  particularly 
important,  yet  it  is  also  difficult,  on  account  of  the  following  fact : 
After  being  grown  in  culture  for  some  time  the  fungus  seems  to 
change  to  a  certain  degree,  at  least,  its  relation  to  the  host  as  a 
parasite,  and  it  is  possible  that  direct  transference  of  the  fungus 
from  one  host  to  another  would  not  yield  the  same  results  as  by 
the  use  of  old  cultures  or  cultures  grown  upon  diverse  media. 

This  fungus  in  all  of  its  forms  is  readily  culturable  upon  the 
ordinary  nutrient  media,  such  as  bean  stems,  potato  and  beet  cylin- 
ders, agars,  corn  meal,  etc.  It  is,  moreover,  not  difficult  to  make 
dilution  cultures,  even  though  the  fungus  usually  grows  upon  those 
parts  of  the  plant  where  bacteria  would  normally  be  present  in 
abundance,  as  upon  roots  and  underground  stems.  By  carefully 
washing  the  mycelium  in  distilled  water  and  then  by  the  use  of 
acidulated  media,  as  suggested  under  cultural  methods,  the  fungus 
may  be  readily  separated  from  contaminating  bacteria. 

Control.  No  effective  preventive  measures  for  the  forms  of  this 
fungus  have  yet  been  found.  It  would  appear,  however,  that  gen- 
eral sanitary  precautions  are  important.  Good  drainage  in  the 
upper  layer  of  the  soil  and  the  presence  of  a  layer  of  sand,  charcoal, 
or  cinders  serve  in  great  measure  to  prevent  the  appearance  of 
the  fungus.  An  aerated  soil  is  also  less  liable  to  be  seriously 
affected,  owing,  perhaps,  to  the  better  health  of  the  roots  than  one 
which  is  poorly  aerated.  The  application  of  lime  and  other  fungi- 
cidal  mixtures  to  a  soil  is  commonly  useless.  This  fungus  is 
apparently  not  readily  affected  either  by  weak  alkalis  or  acids  ;  but 
since  acid  conditions  render  the  host  more  susceptible,  liming  has 
value. 

V.  HEART  ROT  OF  SUGAR  MAPLE 

Hydnum  septentrionale  Fr. 
ATKINSON,  GEO.  F.    Geological  Survey  of  La.  (1889):  335-336.  pi.  38. 

Among  the  numerous  species  of  the  genus  Hydnum,  which 
embrace  the  commoner  toothed  Basidiomycetes,  it  would  seem 


AUTOBASIDIOMYCETES  45  3 

that  few  may  be  classed  as  true  parasites,  the  majority  growing 
upon  logs,  stumps,  etc.,  after  death,  or  after  being  felled.  Some, 
however,  are  unquestionably  in  part  parasitic  to  the  extent  that 
they  may  be  considered  disease-producing  in  woody  plants. 

This  species  occurs  extensively  in  the  United  States,  principally 
on  the  sugar  maple  (Acer  saccharum),  but  also  on  other  species 
of  deciduous  trees.  It  is  likewise  found  generally  distributed  in 
Europe.  The  effects  of  this  fungus  upon  the  wood  of  diseased 
trees  has  not  been  carefully  studied,  but  there  is  certainly  a  heart 
decay,  probably  more  or  less  in  the  manner  of  some  of  the  diseases 
subsequently  described. 

The  sporophores  appear  in  bracket-like  clusters,  which  may  be 
20-30  cm.  wide  and  50-80  cm.  or  more  in  longitudinal  extent. 
The  general  color  is  creamy  white,  and  the  texture  at  first  fleshy, 
becoming  more  fibrous.  The  pileus,  often  3  cm.  thick,  presents  an 
almost  plain  upper  surface,  slightly  scaly,  all  of  the  pilei  being 
united  posteriorly.  Teeth  slender  and  often  12  mm.  long.  This 
is  one  of  the  largest  fungi  in  this  genus,  and  it  is  striking  in 
appearance. 

A  number  of  species  of  this  genus,  or  species  of  closely  related 
genera,  particularly  the  resupinate  forms,  are  found  upon  dead  and 
decaying  wood.  More  beautiful  and  structurally  differentiated  of 
the  Hydnaceae,  such  as  Hydnum  erinaceus,  Hydnum  coralloides, 
etc.,  are  also  found  upon  dead  logs  and  trees  and  sometimes  even 
upon  decayed  portions  of  living  trees. 

VI.    WHITE  ROT  OF  DECIDUOUS  TREES 
Polypfffus  squamosus  (Huds.)  Fr. 

BULLER,  A.  H.  R.  The  Biology  of  Polyporus  squamosus  Huds.,  a  Timber- 
destroying  Fungus.  Journ.  of  Economic  Biology  1  :  101-138.  pis.  5-9. 
1906. 

The  great  scaly  Polyporus,  sometimes  known  as  the  Saddle-back 
fungus,  is  a  tree-destroying  parasite  whose  conspicuous  bracket 
sporophores  are  in  many  regions  well  known  upon  ornamental, 
shade,  and  forest  trees.  The  fungus  occurs  throughout  a  large  por- 
tion of  Europe,  but  it  has  been  found  as  yet  only  sparingly,  it 
would  seem,  in  the  northern  portion  of  the  United  States.  The 


454  FUNGOUS  DISEASES  OF  PLANTS 

distribution  of  this  fungus,  however,  is  doubtless  much  more  ex- 
tensive, although  the  indications  are  that  it  is  uncommon  in  regions 
which  are  rather  dry  throughout  the  summer. 

The  sporophores  of  this  fungus  have  been  reported  upon  various 
species  of  maple  (Acer),  oak  (Quercus),  elm  (Ulmus),  basswood 
(Tilia),  willow  (Salix),  ash  (Fraxinus),  etc.;  therefore  it  may  be  ex- 
pected upon  practically  any  of  the  deciduous  trees.  There  seems 
to  be  no  record  of  its  occurrence  upon  conifers.  The  tree  attacked 


FIG.  223.   POLYPORUS  SQUAMOSUS,  LOWER  SURFACE.    (After  Buller) 

by  this  fungus  dies  gradually,  and  the  effect  may  in  general  be 
called  a  white  rot,  since  there  is  no  marked  discoloration,  and  the 
presence  of  the  mycelium  is  to  lighten  rather  than  darken  the 
effect.  The  hyphae  probably  obtain  entrance  through  wounds,  as  is 
the  case  with  most  other  related  fungi.  The  mycelium  then  grows 
upward  and  downward,  first  in  the  central  portion  of  the  tree, 
apparently  having  little  power  to  affect  directly  the  living  portions. 
It  gradually  works  and  spreads  outward,  killing  the  young  wood 
doubtless  prior  to  invasion,  and  finally  breaking  through  the  sur- 
face and  producing  sporophores  after  a  period  of  years. 


AUTOBASIDIOMYCETES 


455 


The  hyphae  are  hyaline,  considerably  septate,  and  often  show 
clamp  connections  when  growing  in  the  vessels.  They  grow  more 
quickly  in  the  vessels,  but  are  not  ultimately  assembled  into  strands 
in  these  parts.  The  wood  is  eventually  separated  into  plates  or 
cuboidal  areas,  and  the  texture  of  the  wood  becomes  light  and  corky. 
The  separation  of  the  wood  into  plates  is  accomplished  by  the 
growth  of  white  strands  or  bands  of  the  mycelium  in  all  three  direc- 
tions, that  is,  radially,  tangentially,  and  longitudinally.  The  wood 
elements,  which  gradually  disappear  under  the  solvent  action  of 


FlG.  224.    PoLYfORUS  SQUAMOSUS,   UPPER    SURFACE 

the  fungus,  are  largely  those  which  are  less  lignified,  such  as  the 
fibers  between  the  vessels,  that  is,  those  usually  produced  only  dur- 
ing spring  growth.  In  the  dissolution  of  the  cells,  first  the  contents, 
next  the  secondary  cellulose  layer,  and  finally  the  middle  lamellae 
disappear,  so  that  during  the  process  the  cells  do  not  become  sepa- 
rated in  the  early  stages  of  decay. 

The  mycelium  unquestionably  possesses  a  variety  of  enzymes. 
According  to  Buller,  "  from  an  enzymotic  study  of  wood  undergoing 
decay  from  the  agency  of  Polyporus  squamosns  evidence  was  taken 
that  various  enzymes  are  excreted  by  the  fungus  mycelium.  Thus 


456 


FUNGOUS  DISEASES  OF  PLANTS 


the  disappearance  of  starch,  proteids,  and  cellulose  suggests  that 
the  fungus  produces  amylolytic,  proteolytic,  and  cyteolytic  enzymes." 
A  direct  study  of  this  point  was  attempted  by  making  extractions 
from  fresh,  young  fruit  bodies,  and  testing  these.  While  this  may 

not  be  an  absolute  criterion  for 
the  basis  of  an  opinion  as  to  the 
enzymes  produced  in  the  my- 
celium, it  is  nevertheless  inter- 
esting that  laccase,  tyrosinase, 
amylase,  emulsin,  protease, 
lipase,  rennetase,  and  coagu- 
lase  were  seemingly  present, 
"whereas  negative  results  were 
obtained  in  the  tests  for  pec- 
tase,  maltase,  invertase,  treha- 
lase,  and  cytase.  However,  a 
study  of  the  destruction  of  wood 
by  the  fungus  furnishes  evidence 
that  the  mycelium  produces  cy- 
tase and  possibly  hadromase." 

The  sporophores  arise  singly 
or  in  clusters  of  a  few  brackets, 
usually  during  summer  and  early 
autumn.  It  requires  but  a  brief 
period  for  these  sporophores  to 
attain  their  growth,  brackets 
measuring  15—25  cm.  in  width 
having  been  observed  to  com- 
plete growth  within  two  weeks. 
The  mature  sporophore  is  yel- 
lowish brown  above,  and  the 
surface  of  the  cap  is  thrown 
into  characteristic  brown  scales. 
The  plants  are  commonly  15-30  cm.  broad,  although  one  speci- 
men measuring  65  cm.  and  weighing  approximately  six  and  a  half 
pounds  has  been  found  (Buller).  The  margins  of  the  pileus  are 
slightly  revolute  even  on  maturity,  the  lower  surface  of  the  pileus 
yellowish,  with  pores  at  first  small,  later  expanding,  and  angular. 


FIG.  225.  POLYPORUS  SQUAMOSUS:  PRO- 
GRESSIVE DESTRUCTION  OF  WOOD 
(After  Buller) 


AUTOBASIDIOMYCETES  457 

The  flesh  is  white  and  soft  when  young,  becoming  tough  with  age. 
Nevertheless,  this  sporophore  persists  but  a  single  season,  while  a 
diseased  tree  may  continue  to  produce  sporophores  throughout  a 
period  of  years,  and  even  for  some  time  after  having  been  felled. 

In  the  development  of  the  sporophore  a  knob-shaped,  fleshy  body 
appears,  from  which  may  arise  one  or  more  short  stems,  and  the 
changes  in  one  of  the  latter  are  usually  about  as  follows  :  An  apical 
depression  is  the  first  evidence  of  the  pileus.  Further  growth  in 
the  stem  is  hyponastic,  raising  the  depression  toward  the  horizontal, 
and  at  the  same  time  there  is  rapid  and  distinctly  one-sided  lateral 
expansion,  and  later,,  thickening  in  the  region  of  the  depression, 
so  that  it  becomes  a  definite  pileus,  with  the  greatest  growth  on  the 
sides  farthest  from  the  axis  of  attachment,  thus  eventually  giving 
the  excentric  or  almost  lateral  type  of  sporophore. 

The  hymenium  is  very  early  differentiated,  first  as  very  shallow 
reticulations,  but  a  downward  growth  of  the  netted  ridges  develops 
in  time  the  relatively  deep  pores  of  the  mature  sporophore  (Fig.  223). 
The  basidia  and  spores  are  not  unusual  in  form.  The  latter  measure 
about  1 2  x  5  /A.  It  is  not  without  interest  to  note  that  the  spores 
are  forcibly  thrown  from  the  sterigmata  in  this  species,  and  doubt- 
less in  practically  all  other  species  of  Basidiomycetes,  the  form  of 
the  sterigmata  and  the  attachment  of  the  spores  to  these  frequently 
suggesting  the  possibility  of  well-regulated  tensions.  By  a  com- 
paratively accurate  method  Buller  estimated  the  number  of  spores 
produced  in  a  single  pore,  and  found  it  to  be  about  one  million, 
seven  hundred  thousand.  The  spores,  like  those  of  mold  fungi, 
will  withstand  immersion  in  water  for) a  long  period. 

VII.    DECAY,  OR  BROWN  ROT,  OF  TREES 
Polyporus  sulphureus  (Bull.)  Fr. 

ATKINSON,  GEO.  F.  Studies  of  Some  Shade  Tree  and  Timber  Destroying 
Fungi.  Cornell  Agl.  Exp.  Sta.  Built.  193:  208-214.  1901. 

SCHRENK,  H.  VON.  Polyporus  sulfureus  (Bull.)  Fr.  Div.  Veg.  Phys.  and  Path., 
U.  S.  Dept.  Agl.  25:  40-52.  pis.  n  (in  part),  ij.  1900. 

The  sporophores  of  no  other  fungus  present,  probably,  a  more 
striking  appearance  than  the  fresh,  vigorous,  sulfur-yellow  cluster 
of  the  above  species.  It  cannot  be  considered  a  very  virulent 
disease-producing  organism,  in  spite  of  its  wide  distribution  and 


458  FUNGOUS -DISEASES  OF  PLANTS 

the  variety  of  host  plants  upon  which  it  is  reported.  This  fungus 
has  been  found  practically  throughout  the  world  where  trees  grow. 
It  is  unquestionably  more  abundant  in  humid  climates,  yet  minor 
or  nonpersistent,  unfavorable  conditions  do  not  readily  affect  it. 

This  Polyporus  is  of  special  interest  because  of  its  occurrence 
upon  a  large  variety  of  trees.  Deciduous  trees  are  more  commonly 
attacked,  yet  both  in  Europe  and  America  it  is  not  infrequently 
found  upon  conifers.  It  is  perhaps  oftener  noticed  upon  such 


FIG.  226.   POLYPORUS  SULPHUREUS  ON  EXPOSED  ROOTS  OF  A  LIVING  TREE 
(Photograph  by  L.  H.  Childers) 

forest  and  shade  trees  as  oak,  walnut,  butternut,  ash,  black  locust, 
poplar,  and  willow.  Among  orchard  trees  the  cherry  in  old  orchards 
is  a  common  host,  but  pear  and  apple  trees  are  also  susceptible. 
Moreover,  the  sporophores  of  this  fungus  may  appear  upon  fallen 
trunks  and  stumps,  and  it  appears  to  be  true  that  the  mycelium  of 
the  fungus  may  develop  extensively  in  fallen  trunks. 

The  coniferous  trees  upon  which  it  has  been  more  frequently 
observed  are  the  larch  in  Europe  and  the  hemlock  and  spruce  in 
America, 


AUTOJBASIDIOMYCETES 


459 


The  mycelium  evidently  establishes  itself  in  a  saprophytic  man- 
ner upon  dead  branches  or  in  the  decayed  wood  about  knot  holes, 
thence   gaining  entrance   to   the  heartwood   of   the    main  trunk.* 
After  growing  for  years  in  the  latter,  it  may  develop  sporophores 


FlG.  227.     POLYPORUS  SULPHUREUS   ON    WHITE    OAK,    SHOWING    NATURE    OF 

DECAY.    (Photograph  by  Geo.  F.  Atkinson) 

where  wounds  occur,  permitting  the  vigorous  mycelium  to  reach 
the  surface  readily.  In  other  cases  the  path  of  the  mycelium  of  this 
fungus  evidently  extends  directly  to  the  surface,  killing  the  wood 
as  it  progresses.  Sporophores  may  then  be  developed  on  the 
otherwise' uninjured  bark  surface.  In  general,  the  growth  of  the 
mycelium  causes  a  prompt  decay  of  the  wood,  the  latter  becoming 


460  FUNGOUS  DISEASES  OF  PLANTS 

brown  and,  to  a  considerable  extent,  separated  into  plate-like  areas, 
corresponding  in  their  radial  diameters  to  the  seasonal  wood  rings. 
These  plates  are  subsequently  broken  into  smaller  areas  by  lateral 
contact,  and  in  all  of  the  clefts  thus  formed  by  the  processes  indi- 
cated, the  mycelium  often  grows  (especially  in  deciduous  trees)  in 
sheath-like  strata,  the  particular  appearance  of  the  mycelium,  how- 
ever, being  modified  in  different  hosts,  largely  depending  upon  the 
density  of  the  wood  (Fig.  227).  In  all  cases  the  wood  is  brittle  in 
the  last  stages  of  decay  and  may  be  readily  reduced  to  a  powder. 

According  to  von  Schrenk  the  detailed  changes  induced  in  the 
wood  of  the  spruce  may  be  stated  as  follows  : 

Minute  changes  in  the  wood.1  The  minute  changes  which  the  mycelium  of 
Polyporus  sulfureus  induces  in  the  wood  cells  are  such  that  they  cannot  be 
mistaken.  It  has  been  mentioned  that  the  annual  rings  break  into  bands  which 
curve  inward  as  the  process  of  drying  goes  on.  A  tangential  view  of  several 
of  these  bands  before  they  have  broken  will  present  an  appearance  such  as  is 
shown  on  PI.  XI,  fig.  4.  A  large  number  of  fissures  have  formed  both  across 
the  wood  fibers  and  parallel  with  them.  The  latter  are  more  prominent  —  the 
cross  fissures  never  occurring  alone,  but  generally  connecting  several  longi- 
tudinal fissures.  It  will  be  noted  that  the  breaks  are  characterized  by  sharp 
right  angles,  and  in  many  places  a  stepladder  arrangement  is  evident.  In  the 
early  stages  of  attack  the  wood  fibers  turn  red-brown  and  shrink.  As  a  result, 
fissures  are  formed  in  the  walls  of  the  tracheids,  which  extend  diagonally  across 
the  wall  at  an  angle  of  approximately  45  degrees.  (PI.  XI,  fig.  i).  The  med- 
ullary ray  cells  are  at  this  point  still  intact,  and  hold  together  the  more  or  less 
brittle  wood  fibers.  The  next  stage  in  the  decomposition  consists  in*  the  ab- 
sorption of  the  medullary  rays.  This  allows  the  wood  fibers  to  contract  more 
than  up  to  that  time,  and  as  a  result  breaks  occur.  These  breaks  form  at  first 
so  as  to  connect  adjacent  cavities  left  by  the  absorption  of  the  medullary  rays. 
The  wood  fibers  tend  to  curve  in  one  direction  or  another  and  break  at  the 
weakest  point,  namely,  between  two  cavities,  where  the  opportunity  for  curva- 
ture is  greatest.  What  determines  the  direction  of  curvature  of  the  wood  fibers 
has  not  yet  been  explained.  In  the  illustration  the  curvature  is  toward  the 
right.  This  curving  has  the  effect  of  bringing  medullary  rays  which  are  in 
different  longitudinal  rows  approximately  into  a  line.  Thus  at  "  a  "  two  cavi- 
ties are  shown  which  are  separated  by  a  curved  fiber  which  sooner  or  later  will 
break,  uniting  the  two.  At  first  two  ray  cavities  are  joined,  then  more,  until 
long  longitudinal  holes  are  formed,  such  as  are  shown  in  fig.  4  of  PI.  XI.  The 
reason  for  the  sharp  edges  is  now  very  apparent,  likewise  why  these  fissure  fig- 
ures appear  only  on  a  tangential  view,  while  on  the  radial  view  one  simply  sees 
the  fissures  as  lines  extending  at  right  angles  across  a  ring  of  wood  (PI.  XIII). 

1  The  plates  referred  to  are  also  those  of  von  Schrenk's  bulletin. 


AUTOBASIDIOMYCETES  46 1 

On  the  oak  and  other  deciduous  trees  the  mycelium  is  much 
more  dense  than  in  the  spruce,  for  example.  In  the  latter  the 
mycelium  is  said  to  be  colorless.  It  is,  however,  in  some  instances, 
slightly  cream  colored  when  approaching  the  surface.  Hartig 
has  mentioned  the  appearance  of  a  secondary  fruit  form  in  the 
oak.  This  also  occurs  upon  other  hosts,  and  cultures  from  frag- 
ments of  the  sporophore  have  promptly  given,  on  various  culture 
media,  a  vigorous  cream  colored  mycelium,  which  with  age  becomes 
mealy  in  appearance,  due  to  the  extensive  formation  of  conidia, 
such  as  are  referred  to  above.  These  conidia  correspond  to  those 
which  are  considered  by  Brefeld  to  be  the  typical  oidial  stage 
frequently  present  in  Hymenomycetes. 

The  sporophores  of  this  species  appear  usually  during  the  late 
summer  or  early  autumn,  in  large,  shelving  clusters  (Fig.  226)  or 
sometimes  scattered.  The  form  of  the  pileus  may  be  considerably 
modified  by  its  position  upon  the  host  and  by  its  relation  to  other 
sporophores.  The  sporophore  is  fleshy  and  of  a  cheese-like  con- 
sistency when  young,  becoming  harder  and  woodier  with  age.  At 
first  the  entire  sporophore  is  yellow,  but  later  the  under,  pore-bearing 
surfaces  are  bright  yellow,  while  the  upper  surfaces  are  ordinarily 
orange-red.  The  flesh  is  at  first  white,  becoming  slightly  cream 
colored  with  age.  These  sporophores  may  grow  in  such  masses 
as  to  attain  a  length  and  height  of  from  30  to  40  cm.  The  in- 
dividual pilei  may  be  entirely  sessile  or  slightly  stalked,  and  loosely 
scattered  or  so  closely  massed  as  to  be  united  in  the  vicinity  of  the 
host.  The  young  plants  have  a  distinct  odor,  which  becomes  pro- 
nounced with  age.  The  pores  are  found  on  the  under  surface 
only.  They  are  about  4  mm.  deep,  with  nearly  circular  outlines. 
The  spores  are  hyaline,  ovoidal  in  outline,  and  usually  measure 
7-8  x  4-5  /*• 

Control.  In  controlling  this  fungus  the  only  practical  measures 
are  to  cover  up  as  promptly  as  possible  with  tar  or  other  antiseptic 
materials  all  wounds,  either  natural  or  as  a  result  of  pruning,  and 
further,  to  destroy  all  sporophores  as  they  appear.  The  spores  de- 
velop very  quickly  after  the  sporophores  are  mature,  and  it  is  very 
probable  that  their  distribution  is  effected  by  means  of  insects, 
which  may  be  attracted  by  droplets  of  a  sugary  substance  which 
may  accumulate  on  the  under  surfaces  of  the  sporophores. 


462 


FUNGOUS  DISEASES  OF  PLANTS 


VIII.    POLYPORUS:  OTHER  SPECIES 

In  addition  to  the  species  described  at  length,  the  following 
may  be  mentioned  also  as  among  those  of  special  importance, 


FIG.  228.   POLYPORUS  BOREALIS  ON  LIVING  TSUGA.    (Photograph  by 
Geo.  F.  Atkinson) 

occurring  in  Europe  and  in  America,  which  have  received  more 
or  less  recent  consideration  from  the  standpoint  of  shade  and 
forest  tree  diseases. 


AUTOBASIDIOMYCETES 


463 


Polyporus  borealis  (Wahl.)  Fr.  is  a  characteristic  and  destructive 
disease  of  the  spruce  in  Europe,  and  it  occurs  on  a  variety  of  conifers 
in  America.1  The  bracketed  sporophores  are  clustered,  as  shown 
in  Fig.  228.  They  are  fleshy  for  some  time,  but  finally  tough  and 
dry.  The  spores  are  minute,  measuring  4-5  x  3  /u.  The  mycelium 
develops  abundantly  in  the  wood  with  typical  markings  (Fig.  229). 


FIG.  229.  POLYPORUS. BOREALIS:  LONGITUDINAL  SECTION  OF  LOG, 
SHOWING  MYCELIUM.    (Photograph  by  Geo.  F.  Atkinson) 

Polyporus  carneus  Nees  causes 'a  red  rot,  or  peckiness,  in  the 
common  red  cedar  (Juniperus  virginiand)  and  in  the  southern  red 
cedar  (Jimiperus  barbadensis\  as  well  as  in  other  conifers.2 

Polyporus  Juniperinus  von  Schrenk  is  apparently  the  cause  of 
the  white  rot  of  the  red  cedar.2 

Polyporus  Schweinitzii  Fr.  is  abundant  in  Europe  on  the  Scotch 
pine,  Weymouth  pine,  and  the  larch.3  This  species  is  yellowish 

1  Atkinson,  Geo.  F.    Cornell  Agl.  Exp.  Sta.  Built.  193  :  202-208.    1901. 

2  Schrenk,  H.  von.   Div.  Veg.  Phys.  and  Path.,  U.  S.  Dept.  Agl.  Built.  21  :  1-22. 
ph.  7-7.    1900. 

8  Schrenk,  H.  von.   Div.  Veg.  Phys.  and  Path.,  U.  S.  Dept.  Agl.  Built.  25  :  18-24. 


464 


FUNGOUS  DISEASES  OF  PLANTS 


white,  with  little  or  no  stipe,  yellowish  green  pores,  and  spores 
7-8  X  31/4. 

Polyporus  Betulinus  (Bull.)  Fr.  is  the  cause  of  a  sapwood  decay 
in  several  species  of  birch,  and  it  is  very  widely  distributed. 

Polyporus  Fraxinophilus  Pk.,  a  rather  small  white  form  with 
pileus  5-10  X  2.5-4  cm.,  produces  an  important  disease  in  the 
white  ash  (Fraxinus  americana).1 


IX.  FOMES 

ATKINSON,  GEO.  F.  Studies  of  Some  Shade  Tree  and  Timber  Destroying 
Fungi.  Cornell  Agl.  Exp.  Sta.  Built.  193  :  199-235.  figs.  56-94.  1901. 

SCHRENK,  H.  VON.  Diseases  of  Deciduous  Forest  Trees.  Bur.  Plant  Ind., 
U.  S.  Dept.  Agl.  Built.  149:  1-85.  pis.  i-io.  1909. 

The  genus  Fomes  includes 
among  its  representatives  the 
most  destructive  forest-tree 
organisms  in  this  order  of 
fungi.  The  conspicuous 
bracket-like  and  hoof-shaped 
sporophores  are  familiar  to 
all  who  have  given  the  typ- 
ical, temperate  moist  forests 
any  attention.  They  are,  for 
the  most  part,  moisture- 
loving,  wound  fungi ;  and, 
consequently,  they  find  in  the 
conditions  of  the  forest  the 
opportunity  for  their  maxi- 
mum destructiveness.  They 
may  be  entirely  absent  from 
shade  and  meadow  trees. 
Among  many  species  of  com- 
mon  occurrence,  special 
mention  should  be  made  of 
Fomes  igniarius,  Fomes 

FIG.  230.   FOMES  FOMENTARWS  ON  DEAD       fomentarius,   and  Fomes  Pi- 
BEECH.  (Photograph  by  Geo.  F.  Atkinson)       nicola.    Fomes  applanatus  IS 


1  Schrenk,  H.  von.  Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  32  :  1-18.  pis.  1-5.  1903. 


AUTOBASIDIOMYCETES 


465 


FIG.  231.  FOMES  PINICOLA  ON  DEAD  HEMLOCK.    (Photograph  by 
Geo.  F.  Atkinson) 

also  a  conspicuous  form.  Under  the  conditions  now  necessarily 
confronting  those  interested  in  forestry,  there  is  no  practical  method 
of  control.  In  the  woodlot  these  fungi  will  prove  far  less  serious. 
Fomes  igniarius  (L.)  Gillett.  This  species,  commonly  known  as 
the  false  tinder  fungus,  occurs  upon  a  great  variety  of  deciduous 


466 


FUNGOUS  DISEASES  OF  PLANTS 


FlG.  232.     FOMES  APPLANA TUS   ON    HARD    MAPLE:    SMALL    SPECIMENS 

(Photograph  by  Geo.  F.  Atkinson) 

trees.  In  the  moist  forest  it  is  often  difficult  to  find  a  beech 
tree  (Fagus  grandifolid)  ten  inches  or  more  in  diameter  which  is 
not  seriously  affected.  The  fungus  is  also  destructive  to  hard 
maple  (Acer  saccharum),  yellow  birch  (Betula  luted],  aspen  (Popu- 
lus  tremuloides\  and  certain  oaks  (Quercus  spp.)  in  their  ranges. 


AUTOBASIDIOMYCETES  467 

The  sporophore  varies  in  form  from  the  shape  of  a  hoof  to  that 
of  a  thick  bracket.  The  upper  surface  is,  with  age,  black,  indurated, 
and  cracked,  also  showing  concentric  ridges ;  while  the  lower  sur- 
face is  commonly,  during  the  growing  season,  cinnamon-brown. 
The  mycelium  grows  within  the  heartwood,  which  is  generally 
converted  to  a  soft  mass,  bordered  by  black  rings. 

Fomes  fomentarius  (L.)  Fr.  This  fungus  occurs  in  situations 
similar  to  those  mentioned  for  the  preceding  organism.  It  is  far 
more  common  upon  beech,  yellow  birch,  and  hard  maple.  The 
sporophores  may  be  found  upon  living  trees,  but  they  are  produced 
in  far  greater  abundance  after  the  death  of  the  tree  affected.  They  are 
distinctly  hoof-shaped  (Fig.  230),  with  a  grayish  upper  surface  and  a 
lower  surface  which  is  light  brown  or  gray-brown  during  the  summer. 

Fomes  Pinicola  Fr.  In  the  moist  temperate  regions  this  fungus 
induces  a  decay  in  a  variety  of  conifers,  especially  pines  (Finns  spp.), 
spruces  (Picea  spp.),  and  balsam  (Abies  balsamea).  The  sporo- 
phore is  a  broad,  relatively  thick  bracket,  with  a  creamy  white 
under  surface.  The  upper  surface  is  dark,  generally  with  broad 
ridges,  the  lower  of  which  may  be  reddish  to  bright  red-brown 
in  color  (Fig.  231).  The  sporophores  generally  develop  after  the 
death  of  the  tree. 

Fomes  applanatus  (Pers.)  Wallr.  The  sporophores  of  this  fun- 
gus constitute  the  most  conspicuous  forest  brackets.  The  fungus 
occurs  upon  a  variety  of  deciduous  trees,  but  it  is  regarded  as  more 
commonly  saprophytic.  In  any  event,  it  is  important  in  the  decay 
of  trees  injured  by  fire  or  water,  and  of  fallen  trunks. 


X.    A  BROWN  ROT  OF  CONIFERS 
Trametes  Pini  (Brot.)  Fr. 

HARTIG,    R.     Trametes   Pini    Fr.     Wichtige   Krankheiten   der  Waldbaume. 
pp.  43-61.  pi.  j.  figs.  1-19.    1874. 

Among  the  various  species  assigned  to  the  genus  Trametes 
there  are  some  important  wood-destroying  fungi.  Trametes  Pini 
is  common  in  the  United  States  throughout  the  coniferous  forests. 
In  the  Ozark  pine  forests  of  Missouri  it  is  the  chief  cause  of  loss 
from  fungi.  In  some  regions  which  have  been  cut  over  there 
have  been  left  thick  forest  groves,  and  these  often  consist  very 


468  FUNGOUS  DISEASES  OF  PLANTS 

largely  of  trees  that  are  affected  by  this  "  punk."  The  fungus  is 
also  common  in  pine  forests  of  northern  Europe,  occurring  there, 
as  well  as  in  parts  of  America,  on  the  spruce.  According  to 
Hartig,  trees  are  more  subject  to  this  fungus  in  woods  exposed  to 
strong  winds,  since  the  breaking  of  limbs  of  older  trees  by  any 
cause  invites  infection. 

The  phenomenon  of  infection  and  the  spread  of  the  fungus 
within  the  tree  are  doubtless  accomplished  in  a  manner  similar  to 
the  cases  already  described.  The  wood  pervaded  by  the  fungus 
assumes  from  the  first  a  deep  red-brown  color.  There  is  no 
checking,  in  the  proper  sense,  although  occasionally  the  annular 
rings  may  in  one  or  more  regions  be  readily  separable.  The  chief 
characteristic,  however,  so  far  as  the  effect  upon  the  wood  is  con- 
cerned, is  to  be  found  in  the  development  of  bleached  pits  or 
pockets.  The  formation  of  these  may  be  readily  understood  when 
it  is  ascertained  that  the  action  of  the  mycelium  is  first  to  delignify 
the  cells,  then  to  dissolve  the  middle  lamellae,  so  that  the  cells  are 
set  free  prior  to  general  dissolution.  The  wood  is  therefore  in 
certain  areas  transformed  to  more  or  less  pure  cellulose  and  con- 
sequently bleached  in  appearance.  The  pockets  appear  more  or 
less  circular  in  cross  section,  and  vary  in  shape  from  ovoidal  to 
long-cylindrical.  The  pockets  are  at  first  to  be  found  chiefly  in  the 
spring  wood  portion  of  the  annular  ring.  The  mycelium  is  yel- 
lowish in  color  and  is  not  massed  in  strands  in  the  pockets. 

In  the  pine  the  sporophore  is  almost  invariably  formed  in  a 
wounded  area,  and  the  fruit  body  may  be  in  the  form  of  an  in- 
crusted,  brown-black  stratum,  or  as  a  hoof-shaped  bracket.  These 
sporophores  are  perennial,  and  for  a  few  years  the  annular  layers 
which  are  developed  successively  upon  the  fruiting  surfaces  in- 
crease the  size  of  the  fruit  body.  Subsequently,  however,  there 
may  be  no  increase  in  size  from  the  deposition  of  new  layers,  or 
the  strata  may  be  of  smaller  extent,  in  case  of  the  death  of  a  por- 
tion of  the  last-formed  annular  layer.  The  fruit  body  may  attain 
a  considerable  age,  and  each  year  or  season  of  growth  will  be  out- 
lined by  a  somewhat  prominent  concentric  ring,  or  surface  ridge. 
The  lower  or  marginal  ridge,  including  the  hymenial  surface,  is  of 
a  light  brown  color,  but  older  ridges  become  black  and  very  irregular 
in  outline,  A  section  of  a  sporophore  shows  a  layered  structure, 


AUTOBASIDIOMYCETES  469 

corresponding  to  the  surface  rings.  The  new  growth  apparently 
takes  place  from  all  exposed  surfaces  which  are  still  corky  in  tex- 
ture, including  the  lower  margins  of  the  sporophores.  Doubtless 
the  sterile  basidia  continue  their  growth  as  vegetative  hyphae.  The 
sporophores  may  be  produced  high  upon  the  trunks,  and  since  an 
annual  crop  of  spores  is  produced,  they  are  most  favorably  situated 
to  be  blown  upon  other  trees.  Young  conifers  are  in  part  protected 
from  infection  by  the  resinous  exudates  which  form  over  wounds. 
Control.  No  method  of  controlling  this  fungus  is  possible,  ex- 
cept by  preventing,  as  far  as  may  be,  the  causes  leading  to  the 
breaking  of  living  branches.  In  well-cared-for  forests  it  is  practi- 
cable to -fell  diseased  trees  as  promptly  as  possible  or  to  destroy 
developing  sporophores. 

XI.    ROOT  DISEASE  OF  SUGAR  CANE 
Marasmius  plicatus  Wakker. 

COBB,  N.  A.    Fungus  Maladies  of  the  Sugar  Cane.    Hawaiian  Sugar  Planters' 

Exp.  Sta.,  Div.  Path,  and  Phys.  Built.  6  :    no  pp.  (cf.  24-26,  50).  1906. 
FULTON,  H.  R.    The  Root  Disease  of  Sugar  Cane.    La.  Agl.  Exp.  Sta.  Built. 

100:    i -21.  figs.  1-8.    1908. 
HOWARD,  A.    On  Some  Diseases  of  the  Sugar  Cane  in  the  West  Indies. 

Ann.  Bot.  17:  373-411.  pi.  18.    1903. 
WAKKER,  J.  H.    Eine  Zuckerrohrkrankheit,  verursacht  durch  Marasmius  Sac- 

chari  n.  sp.    Centrbl.  f.  Bakt,  Par.  und  Infektionskr.  2  (Abt.  2) :  44-56. 
Jigs.  7-5.    1896. 

A  root  disease  of  the  sugar  cane  in  Java  was  first  described  by 
Wakker,  and  the  causal  fungus  was  given  as  Marasmius  Sacchari. 
A  similar  disease  was  subsequently  found  in  other  portions  of  the 
West  Indies,  in  the  Hawaiian  Islands,  and  recently  in  Louisiana. 
It  is  now  known  to  be  widely  distributed  in  the  southern  United 
States.  From  the  work  which  has  been  done  thus  far  it  seems 
apparent  that  several  species  of  Marasmius  may  be  concerned  in 
the  production  of  a  more  or  less  common  type  of  root  disease.  In 
all  cases  the  fungus  appears  to  be  merely  a  weak  parasite,  and  it 
frequently  gains  entrance  to  the  host  through  the  wounds  upon 
cuttings  and  seed  plants. 

Symptoms.  Stools  of  the  sugar  cane  affected  by  this  fungus 
are  commonly  smaller  and  poorly  rooted,  so  that  the  disease  be- 
comes especially  evident  during  conditions  of  drought 


470 


FUNGOUS  DISEASES  OF  PLANTS 


Having  gained  entrance  through  the  stubble  or  plant  canes  the 
fungus  invests  the  root  system,  and  also  the  lower  joints  of  the 
stem,  cementing  the  leaf  sheaths  together  near  the  base  with  a 
whitish  mycelium.  Not  only  is  great  injury  done  to  the  growing 
stools,  but  a  vastly  greater  loss  results  from  missing  hills  of  cane, 
on  account  of  the  fact  that  the  diseased  stubble,  or  plant  canes, 

may  be  so  covered  up  by  the 
fungus  that  few  stalks  will  be 
produced. 

The  fungus.  Under  favor- 
able conditions  (constant  mois- 
ture being  indispensable),  the 
mycelium  which  is  constantly 
associated  with  the  root  dis- 
ease may  develop  fruit  bodies, 
or  sporophores.  The  type  of 
sporophore  in  the  case  of  the 
Louisiana  disease  is  shown  in 
Fig.  233.  It  is  described  by 
Fulton  as  follows : 

The  pileus  is  dirty  white,  becom- 
ing somewhat  darker  with  age ;  it  is 
usually  about  three  fourths  of  an  inch 
in  diameter,  but  may  attain  a  size  of 
an  inch  and  one  fourth.  When 
young  it  is  convex,  and  at  maturity 
is  almost  flat  or  perhaps  slightly  con- 
cave. Its  surface  is  smooth.  On 
the  under  side  are  the  radiating  gills 
which  have  an  even,  thin  edge,  and 
a  straight,  radial  direction.  The  long 

gills  extend  from  the  margin  to  the  stein,  and  are  attached  to  the  stalk  itself 
rather  than  to  a  prominent  ring  about  the  stalk.  Other  shorter  gills  extend 
from  the  margin  just  far  enough  to  fill  in  the  angles  between  the  longer  gills. 
The  stipe  is  about  equal  in  length  to  the  diameter  of  the  cap,  or  in  some  cases 
somewhat  less.  It  usually  arises  from  the  side  of  the  leaf  sheath,  and  is  some- 
what curved  so  as  to  bring  the  cap  into  a  horizontal  position.  It  is  normally 
attached  to  the  cap  at  its  central  point,  but  at  times  this .  attachment  is  some- 
what eccentric.  The  stipe  is  smooth  externally,  except  at  the  base,  which  is 
downy  and  also  enlarged.  The  whole  fruit  cap  persists  for  about  a  day,  and  then 
gradually  dries,  losing  its  form,  but  not  undergoing  immediate  disintegration. 


FIG.  233.   MARASMIUS  PLICATUS  ON 

SUGAR   CANE.    (Photograph  by 

H.  R.  Fulton) 


AUTOBASIDIOMYCETES  47 1 

The  spores,  white  in  mass,  are  hyaline,  ovate,  averaging  6-8  x 
5-6  ft,  with  a  prolongation  at  the  base.  The  fungus  has  been 
grown  in  pure  cultures,  and  inoculation  experiments  from  such 
pure  cultures  have  yielded  the  typical  disease,  this  in  turn  show- 
ing the  characteristic  mycelium.  The  mycelium  in  culture  makes 
the  best  growth  at  from  25°  to  30°  C.  The  fungus  spreads  rapidly 
by  means  of  the  vigorous  mycelium,  and  the  sporophores  are  pro- 
duced so  infrequently  that  spores  would  seem  to  play  a  minor  part 
in  the  distribution  of  the  species. 

Control.  As  a  result  of  his  studies,  Fulton  cites  the  following 
conditions  as  favoring  the  growth  of  the  organism. 

1 .  Slowness  of  germination  and  early  growth  of  the  canes. 

2.  Improper  cultural  procedures. 

3.  Unsuitable  soil. 

4.  Bad  drainage. 

5.  Unfavorable  seasonal  conditions. 

6.  A  stubble  crop. 

These  facts  make  it  evident  that  prevention  should  be  concerned 
with  general  methods  of  sanitation,  such  as  the  destruction  of  all 
infected  waste  material,  the  rotation  of  crops,  selection  and  disin- 
fection of  seed  cane,  and  also  the  planting  of  the  more  resistant 
varieties. 

XII.    ROOT  ROT  OF  FRUIT  TREES 
Clitocybe  parasitica  Wilcox 

WILCOX,  E.  M.    A  Rhizomorphic  Root-Rot  of/ Fruit  Trees.    Okla.  Agl.  Exp. 
Sta.  Built.  49:    1-32.  pis.  i-n.    1901. 

For  some  years  attention  has  been  called  to  a  destructive  disease 
of  apple  trees  in  Missouri,  Oklahoma,  and  adjacent  states,  character- 
ized primarily  by  the  death  of  the  root  system.  There  is  commonly 
associated  with  this  disease  an  invasion  of  the  root  system  by  the 
mycelium  of  some  one  of  the  mushrooms.  Wilcox  has  concluded 
that  the  disease  in  Oklahoma  is  caused  by  a  fungus  described  as 
a  new  species,  Clitocybe  parasitica.  He  has  found  this  fungus 
constantly  associated  with  the  root  rot  of  the  apple,  and  also  with 
a  similar  disease  of  peach  and  cherry,  as^  well  as  of  certain  native 
species  of  oak.  Other  observers  have  apparently  not  been  able 
to  conclude  that  a  Clitocybe  is  the  cause  of  the  disease  prevalent 


472  FUNGOUS  DISEASES  OF  PLANTS 

throughout  that  general  region,  and  now  notably  destructive  in 
sections  of  Missouri.  At  any  rate  this  species  of  Clitocybe  is  very 
common  at  least  from  Missouri  south  westward,  and  occurs  abun- 
dantly in  regions  in  which  the  root  rot  of  apples  is  unknown.  This 
fungus  occurs,  for  instance,  during  a  favorable  season  in  unlimited 
quantity  at  Columbia,  Mo.,  and  may  be  found  arising  in  large 
clusters  from  the  roots  of  hickory  and  other  deciduous  trees  ;  but 
no  evidence  in  that  vicinity  of  its  appearance  in  orchards  has 
come  to  the  attention  of  the  writer,  although  constant  search  has 
been  made  for  it, ,  particularly  where  orchards  have  succeeded 


FIG.  234.    CLITOCYBE  PARASITICA:  A  CLUSTER  OF  SPOROPHORES  FROM 
ROOT  OF  HICKORY 

deciduous  forests.  The  Clitocybe  is  unquestionably,  however,  an 
injurious  fungus,  and  it  is  quite  possible  that  the  failure  to  attack 
apples  in  certain  regions  is  due  to  more  favorable  conditions  for 
the  host. 

The  fungus  shown  in  Fig.  234  grows  in  very  dense  clusters. 
The  pileus  is  usually  from  6  to  8  cm.  in  diameter,  convex  or 
umbonate  in  form,  usually  beset  with  minute  scales,  varying  in 
color  from  mottled  buff  to  pale  yellowish  brown.  The  gills  are  paler 
and  become  mottled,  noticeably  decurrent  at  first,  which  charac- 
ter is  still  slightly  evident  with  age.  The  stipe  is  usually  10-16  cm. 
in  length,  and  up  to  I  cm.  in  diameter,  solid,  usually  curved,  and 


AUTOBASIDIOMYCETES  473 

somewhat  darker  in  color  than  the  pileus.  Rhizomorphs  are  pres- 
ent, and  these,  at  maturity,  are  black  in  color.  When  growing 
close  beside  the  trunk  or  under  the  edge  of  fallen  logs  or  brush, 
giant  forms  of  the  mushroom  may  appear,  single  specimens  of 
which  have  been  found  weighing  more  than  a  pound,  with  gills 
anastomosing  and  variously  modified.  It  has  been  suggested  by 
some  observers  that  Agaricus  melleus  is  responsible  for  this  root 
rot  of  the  apple,  but  the  writer  has  never  detected  this  fungus 
associated  with  the  typical  disease  in  Missouri. 

Control.  It  is  hardly  possible  to  adopt  effective  control  measures, 
but  it  is  desirable  that  every  means  possible  be  taken  to  get  rid 
of  stumps  and  roots  in  land  set  to  an  orchard,  and  preferably 
such  land  should  be  grown  to  some  grain  or  other  field  crop  for 
several  years  previous  to  its  use  for  orchard  purposes.  Isolation 
of  affected  trees  by  trenching,  and  the  prompt  removal  and  de- 
struction of  these,  is  also  to  be  recommended. 

XIII.    THE  HONEY  AGARIC 
Armillaria  melka  Vahl. 

HARTIG,  R.    Wichtige  Krankheiten  der  Waldbaume.  pp.  12-42.  pis.  I,  2. 
HARTIG,  R.    Die  Zersetzungserscheinungen  d.  Holzes  d.  Nadelholzbaume  u.  d. 
Eiche.   Berlin,  1878. 

Of  the  Agaricacea^  which  may  induce  plant  diseases  there  is  no 
fungus  better  known  or  more  destructive  tjian  Armillaria  mellea. 
It  is  abundant  in  Europe  and  America,  aiid  doubtless  has  a  very 
general  distribution.  This  fungus  is  unusual  in  that  it  is  no  less 
common  as  a  saprophyte  than  as  a  parasite.  It  is  said  to  occur 
upon  all  conifers  which  grow  in  Europe,  and,  among  deciduous 
trees,  especially  upon  Primus  aviiim  and  Prunus  domes  tic  a.  In 
moist  regions  it  has  been  noted  upon  a  variety  of  hosts,  and  in 
the  small  forests  of  central  Missouri  it  has  done  greatest  damage 
to  young  trees  of  the  hop  hornbeam  (Ostrya  virginiand]  and  of 
the  white  oak  (Qtiercus  alba}.  It  frequently  attacks  saplings,  or  at 
least  its  effects  become  evident  upon  such  trees,  of  from  \\  to 
3  in.  in  diameter.  Infested  trees  grow  very  slowly,  and  often  the 
leaves  fall  in  early  summer.  When  so  far  affected  death  promptly 
ensues,  An  examination  of  the  crown  of  these  trees  would  show 


474 


FUNGOUS  DISEASES  OF  PLANTS 


a  considerably  advanced  stage  of  decay  in  the  region  of  the  cam- 
bium, including  both  wood  and  bark.  There  is  present  an  abundant 
white  mycelium  and  very  characteristic  mycelial  strands,  as  subse- 
quently described. 

The  abundant,  white  mycelium  is  particularly  rich  in  stored 
nutrients.  It  commonly  extends  several  feet  above  the  crown, 
mostly  between  the  wood  and  bark.  The  characteristic  mycelial 
cords,  by  which  this  fungus  is  best  known,  are  shining,  gray-black 


FIG.  235.  ARMILLARIA  MELLEA  ON  A  STUMP  OF  WHITE  OAK 
(Photograph  by  Geo.  F.  Atkinson) 

strands  which  may  measure  from  I  to  2\  mm.  in  diameter.  They 
are  typical  rhizomorphs.  These  begin  as  complex  hyphal  masses 
which  become  readily  sclerotial  in  character.  These  strands  attain 
enormous  lengths.  They  may  course  upward  and  downward  in  the 
affected  tree,  generally  under  the  bark,  or  merely  in  close  contact 
with  the  outer  surface  of  the  bark.  They  also  grow  through  the 
soil  to  considerable  distances,  thus  serving  to  spread  the  disease 
to  neighboring  trees.  According  to  Hartig  this  strand  is  differ- 
entiated near  the  apex  into  several  layers.  The  outer,  more  gelati- 
nous layer  becomes  somewhat  horny  ;  some  loose  hyphas,  however. 


AUTOBASIDIOMYCETES  475 

extend  outward,  perpendicular  to  this  sheath.  Within  this  zone 
there  is  next  found  a  dense,  resistant  layer  of  small-celled  pseudo- 
parenchymatous  tissue,  surrounding  a  medullary  cylinder  com- 
posed of  lighter,  more  delicate,  conducting  cells.  At  the  base  of 
the  tree  the  general  mycelium  produces  a  definite  white  rot. 

In  this  country  sporophores  are  usually  produced  during  favor- 
able weather  in  September,  October,  and  early  November.  They 
may  appear  at  the  collar  of  the  tree,  or  upon  the  roots,  etc.  More- 
over, a  year  or  two  after  forest  land  has  been  cleared  for  pasturage, 
the  sporophores  may  appear  in  enormous  quantities  on  the  slightly 
sunken  roots.  These  fruit  bodies  are  usually  produced  in  clusters, 


FIG.  236.   ARMILLARIA  MELLEA  ON  EXPOSED  ROOTS  IN  A  MEADOW 

arising  either  directly  from  a  felted  mycelium  or  from  rhizomor- 
phal  aggregations.  The  mature  sporophore  (Fig.  236)  consists  of 
a  fleshy  cap,  ordinarily  5-15  cm.  broad,  borne  upon  a  central  stalk 
often  1 2- 1 8  cm.  long,  with  cartilaginous  rind  and  spongy  center. 
The  stem  is  yellowish  in  color  above,  but  usually  brown  below,  with 
a  more  or  less  persistent  annulus,  or  attached  collar.  The  cap  varies 
from  convex  to  slightly  umbonate.  It  is  yellow  to  orange-brown  in 
color,  the  center  of  the  cap  when  younger  being  often  covered  with 
papilliform,  brown,  or  sooty  scales.  The  lamellae  are  white  or  slightly 
discolored,  distinct  one  from  another,  and  somewhat  decurrent  upon 
the  stem.  In  taste  this  plant  is  distinctly  acrid,  sometimes  very 
harsh.  It  is,  however,  considered  to  be  edible  by  those  who  have 
developed  a  taste  for  a  variety  of  mushroom  flavors. 


476  FUNGOUS  DISEASES  OF  PLANTS 

With  reference  to  the  development  of  the  sporophore,  the  early 
studies  of  Hartig  would  indicate  that  it  begins  as  an  ovoidal  or 
spheroidal  body,  made  up  of  closely  united  hyphae,  the  direction 
of  whose  growth  is  soon  mostly  longitudinal.  For  some  time  there 
is  no  differentiation  of  stem  and  cap,  but  after  the  hyphal  mass  has 
attained  a  length  of  several  millimeters,  differentiation  into  these 
parts  becomes  evident.  In  the  first  place,  an  annular  furrow  is 
formed  by  cessation  of  growth  in  certain  filaments  near  the  apex, 
and  this  annular  furrow  delimits  pileus  and  stipe.  Subsequently, 


FIG.  237.   ARMILLARIA  MELLEA:  RHIZOMORPHS  AND  YOUNG  SPOROPHORES 
(Photograph  by  H.  H.  Whetzel) 

the  outer  layer  of  filaments  from  below  and  from  above  this  fur- 
row become  interlaced,  and  thus  is  formed  an  early  stage  of  the 
veil,  or  membrane,  inclosing  the  area  in  which  the  hymenium  is 
eventually  produced.  As  growth  proceeds,  the  overlapping  periph- 
eral elements  become  wholly  indistinguishable,  the  pileus  is  then 
developed  by  successions  of  epinastic  and  hyponastic  growth,  the 
principal  growth  being  in  the  direction  of  the  pileus.  The  hyme- 
nial  surface  is  thereafter  differentiated  by  the  growth  downward  of 
alternating  radial  hyphal  bands,  which  form  the  trama,  or  middle 
tissue  of  the  lamella,  bearing  eventually  the  hymenium  or  surface 
from  which  the  basidia  are  produced.  With  the  rapid  growth  in 


AUTOBASIDIOMYCETES  477 

the  lower,  or  lamellar,  portion  of  the  pileus,  the  cap  is  quickly  raised 
and  the  veil  broken  at  the  margins  of  the  pileus,  with  the  gradual 
expansion  of  the  upper  portion  of  the  plant.  This  general  form  of 
development  apparently  maintains  in  most  angiocarpic  Agaricaceae 


FIG.  238.  ARMILLARIA  MELLEA:  BASIDIAL  SURFACE.    (After  Hartig) 

which  possess  a  veil  only.  Differences  occur,  however,  with  regard 
to  the  time  of  differentiation,  position  of  the  forming  lamellae,  the 
stem,  veil,  etc. 

XIV.    EUROPEAN  ROOT  DISEASE  OF  ALFALFA  AND 
OTHER  PLANTS 

Rhizoctonia  Medicaginis  D£  C. 

FRANK,  A.  B.   Die  Pilzparisitaren  Krankheiten  der  Pflanzen,  /.  ^.,  pp.  514-518. 

KUHN,  J.    Die  Krankheiten  der  Kulturgewachse,  /.  c.,  p.  245. 

TULASNE,  L.  R.  and  C.    Rhizoctonia.    Fungi  Hypogaei,  I.e.,  pp.  188-195, 

De  Candolle  described  accurately  the  root  disease  of  alfalfa 
(Medicago  sativa)  in  1815,  and  gave  to  the  violet  fungus  pro- 
ducing the  disease  the  name  above  indicated.  The  fungus  had 
previously  passed  under  another  name,  which,  however,  probably 
referred  to  several  diverse  species.  From  the  subsequent  work  of 
Ktihn,  Frank,  Comes,  and  others,  much  additional  information  has 
been  presented  concerning  this  fungus.  Many,  however,  have  re- 
garded it  as  closely  related  to  certain  sterile  fungi  found  upon 
the  crocus,  potato,  cabbage,  sugar  beet,  and  many  other  cultivated 


478 


FUNGOUS  DISEASES  OF  PLANTS 


and  wild  plants.  The  last-mentioned  fungi  are  at  least  closely 
related,  perhaps  forms  of  a  single  species ;  and  in  this  treatise 
they  are  provisionally  referred  to  the  genus  Corticium.  They  have 
been  discussed  under  Corticium  vagum  B.  &  C.,  var.  Solani  Burt. 

The  writer  examined  various 
diseases  due  to  Rhizoctonia 
while  in  Europe  during  1899 
and  1900,  and  subsequently 
in  the  United  States.  As  a 
result,  certain  observations 
may  be  stated.  In  the  first 
place,  the  common  alfalfa 
root  fungus  of  Europe  (R/ii- 
zoctonia  Medicaginis]  is  the 
same  as  the  European  root 
fungus  of  asparagus  (Aspara- 
gus officinalis}.  This  species 
also  occurs  less  frequently 
upon  the  sugar  beet  (Beta 
vulgaris\  and,  doubtless, 
upon  other  cultivated  and 
wild  plants.  The  fungus  ap- 
pears upon  the  root  as  a  close 
weft  of  violet-colored  hyphae 
(Fig.  239),  composed  of  cells 
more  or  less  uniform  in  diam- 
eter, filamentous,  branched, 
but  without  a  particularly 
characteristic  type  of  branch- 
ing. Morphologically,  it 
bears  no  resemblance  to  the 
sterile  stage  of  Corticium 
vagum,  above  referred  to, 
that  is,  the  form  causing  the  rot  of  the  crocus,  and  a  similar  disease 
of  the  carrot,  etc.,  in  Europe,  the  rot  of  beets,  stem  rot  of  carna- 
tions, certain  damping-off-diseases,  etc.,  in  America. 

Rhisoctonia  Medicaginis  does  not  occur  in  America  so  far  as 
can  be  ascertained.    In  Europe  it  is  one  of  the  most  destructive 


FIG.  239.   RHIZOCTONIA  MEDICAGINIS  ON 
ROOTS  OF  ASPARAGUS 


AUTOBASIDIOMYCETES  479 

of  the  clover  diseases  and  frequently  becomes  epidemic  in  planta- 
tions of  alfalfa,  or  lucern,  a  highly  important  forage  plant  of 
Central  Europe.  In  asparagus  growing  the  losses  are  also  occa- 
sionally severe. 

An  ascomycetous  fungus  occurring  upon  the  stubble  of  alfalfa, 
described  as  Leptosphceria  circinans  Fckl.,  has  been  by  some  re- 
garded as  the  perfect  stage  of  Rhizoctonia  Medicaginis,  yet 
through  cultures  of  ascospores  the  writer  has  been  unable  to  pro- 
duce a  mycelium  resembling  that  of  the  Rhizoctonia.  Moreover, 
the  mycelium  of  the  Rhizoctonia  has  been  unusually  difficult  to 
propagate  in  artificial  cultures. 

XV.    ROOT  ROT  OF  COTTON  AND  ALFALFA 
Ozonium  omnivorum  Shear 

ATKINSON,  GEO.  F.  Method  for  Obtaining  Pure  Cultures  of  Pammel's  Fun- 
gus of  Texas  Root  Rot  of  Cotton.  Bot.  Gaz.  18  :  16-19.  l&93- 

PAMMEL,  L.  H.  Cotton  Root  Rot.  Texas  Agl.  Exp.  Sta.  Rept.  2:  61-86. 
1889.  (Also  published  as  Built.  7:  1-30.  1889.) 

SHEAR,  C.  L.,  and  MILES,  G.  F.  The  Control  of  Texas  Root  Rot  of  Cotton. 
Bur.  Plant  Ind.,  U.  S.  Dept.  Agl.  Built.  102  (Pt.  5):  39-42.  1907. 

In  Texas  and  other  neighboring  states  a  serious  root  rot  of  cot- 
ton (Gossypium  spp.)  and  alfalfa  (Medicago  sativa)  has  been  known 
for  a  number  of  years.  It  is  not,  however,  confined  to  these  hosts, 
and  among  cultivated  plants  the  sweet  potato  (Ipomcea  Batatas]  is 
also  affected.  Pammel  in  1 889  reported  it  on  ten  or  more  deciduous 
trees  and  also  on  a  few  herbaceous  weeds.  During  the  summer  of 
1901  I  found  this  fungus  on  twelve  different  weeds  in  a  single 
cotton  field  near  Paris,  Texas.  Since  these  hosts  represent  a 
number  of  widely  separated  orders,  it  is  apparent  that  the  fungus 
is  practically  unrestricted.  It  does  not,  however,  seem  to  occur 
upon  monocotyledonous  plants. 

Little  is  known  about  infection  and  the  progressive  stages  of 
the  disease.  There  is  apparently  very  little  evidence  of  the  trouble 
until  the  plant  suddenly  wilts  and  dries  up.  It  would  seem  that 
cotton  plants  are  far  more  commonly  killed  after  some  of  the  bolls 
begin  to  mature.  Certainly  dead  stalks  become  more  evident  from 
this  time  forward.  Nevertheless,  plants  have  been  killed  by  the 
fungus  before  even  any  definite  flower  buds,  or  squares,  have 


480 


FUNGOUS  DISEASES  OF  PLANTS 


appeared.  An  examination  of  the  plant  after  death  shows  that  all 
of  the  smaller  roots  have  been  killed,  and  these  readily  break  off 
as  the  plant  is  pulled  from  the  soil.  At  this  time  the  main  root 
as  well  as  the  fibrous  root  system  is  infested  with  a  weft,  or  with 
strands,  of  the  dirty  yellow  or  buff -colored  fungus. 

The  mycelium  penetrates  the  bark  and  also  the  wood  of  the 
roots.  It  does  not,  however,  extend  into  the  wood  far  above  the 

surface  of  the  soil.  This 
organism  in  the  United 
States  was  first  studied  by 
Pammel  and  provisionally 
referred  by  him  to  the  ster- 
ile form  Ozonium  aurico- 
mum  Lk.  He  seems  to 
have  had  doubt  of  the  cor- 
rectness of  this  reference 
from  the  beginning,  and 
Shear  now  regards  this 
American  fungus  as  one 
clearly  distinct  from 
Link's  species,  and  he  has 
accordingly  given  it  a  new 
specific  name,  as  above. 

This  fungus  may  be 
grown  on  cooked  potato 
and  other  nutrient  media, 
but  the  organism  is  none 
too  readily  isolated.  No 
spore  stage  has  been  found 
in  culture,  nor  definitely 
associated  with  it  in  the 
open.  A  careful  study  of 
the  organism  in  the  field  has  given  indications,  however,  that  an 
oidium  stage  may  be  developed  under  certain  conditions,  and  that 
the  organism  is  probably  a  Basidiomycete. 

It  seems  that  no  successful  inoculation  experiments  have  been 
reported  with  this  fungus.  During  two  seasons  I  attempted  to 
transfer  the  disease  to  potted  cotton  plants  in  the  greenhouse. 


FIG.  240.    OZONIUM  OMNIVORUM  ON  ROOTS 
OF  COTTON 


AUTOBASIDIOMYCETES  48 1 

Diseased  roots  of  cotton  and  alfalfa,  showing  an  abundance  of  the 
fungus,  were  placed  beneath  the  soil  in  contact  with  the  healthy 
roots  of  half-grown  plants.  In  every  case  the  fungus  failed  to 
spread,  and  after  a  few  months  seemed  to  be  dead.  These  experi- 
ments, however,  were  merely  preliminary,  and  the  conditions  under 
which  the  tests  were  made  could  not  be  considered  satisfactory. 

Control  measures.  Control  measures,  according  to  Shear,  should 
concern  themselves  primarily  with  proper  aeration  of  the  soil,  espe- 
cially deep  preparation  and  as  close  cultivation  as  may  be  compatible 
with  other  requirements.  Fall  plowing,  under  circumstances  where 
this  can  be  practiced  without  injury  to  the  land,  is  advised.  This 
is  particularly  applicable  when  short  rotations  are  impossible. 
Rotation  of  crops  is  especially  important.  Grain  crops  and  others 
known  to  be  free  from  the  fungus  should  alternate  with  cotton. 
An  application  of  a  fungicide  to  the  soil  at  the  time  of  planting 
seems  to  be  neither  effective  nor  practicable. 


HOST  INDEX  OF  FUNGOUS  DISEASES  SPECIALLY 
DESCRIBED  OR  CITED 

Acacia  (Acacia  spp.)  PAGE 

Rust,  Uromyces  tepperianus  Sacc 393 

Alfalfa  (Medicago  sativa  L.) 

Anthracnose,  Colletotrichum  Trifolii  Bain 328 

Leaf  Spot,  Pseudopeziza  Medicaginis  (Lib.)  Sacc 203 

Root  Gall,  Urophlyctis  Alfalfce  (v.  Lagerh.)  Magn 140 

Root  Disease,  European,  Rhizoctonia  Medicaginis  De  C. 477 

Root  Rot,  Ozonium  omnivorum  Shear 479 

Ambrosia  (Ambrosia  spp.) 

Leaf  Blight,  or  Smut,  Entyloma  compositarum  Farl 381 

Almond  (Primus  Amygdalus  Baill.) 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     .     .     .  114 

Leaf  Blight,  Cercospora  circumscissa  Sacc 314 

Rust,  Puce in ia  Pruni-spinosce  Pers 417 

Ampelopsis  (Ampelopsis  spp.) 

Leaf  Spot,  Phyllosticta  Ampelopsidis  Ell.  &  Mart 347 

Anemone  (Anemone  spp.) 

£         (Puccm ia  fusca  Relhan       422 

\Puccinia  Pruni-spinosa  Pers 417 

Sclerotial  Disease,  Sclerotinia  tuberosa  (Hedw.)  Fckl 201 

Apple  (Pyrus  Mains  L.) 

Anthracnose,  or  Bitter  Rot,  Glomerella  rufomaculans  (Berk.)  Spauld.  & 

von  Schrenk 271 

Baldwin  Fruit  Spot,  Cylindrosporium  Pomi  Brooks 341 

Black  Rot,  Sphceropsis  Malorum  Pk.    .    .    .    / 350 

Blight,  Fire  Blight,  Twig  Blight,  Bacillus  amylovorus  (Burr.)  De  Toni  .  121 

Blotch,  Phyllosticta  solitaria  E.  &  E 346 

(Bacillus  amylovorus  (Burr.)  De  Toni 121 

Nectria  cinnabarina  (Tode)  Fr 239 

Canker  «|  Nectria  ditissima  Tul 242 

Nummularia  discreta  Tul.     .     . 282 

\^Sph(zropsis  Malorum  Pk 350 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Fly  Speck,  Leptothyrium  Pomi  (Mont.  &  Fr.)  Sacc 367 

Fruit  Mold,  or  Brown  Rot,  Sclerotinia  fructigena  (Pers.)  Schroet  .     .    .  187 

Leaf  Spot  (Phyllosticta  Pyrina  Sacc 347 

\Sph<zropsis  Malorum  Pk .    .    .    .     .     .  350 

Pink  Rot,  Cephalothecium  roseum  Cda ,    ,    .     .    .  295 

483 


484  HOST  INDEX  OF  FUNGOUS  DISEASES 

PAGE 
Apple  (PyrusMalus  L.)  (Continued) 

(Podosphara  Oxyacantha  (DeC.)  De  Bary      ....  226 

Powdery  Mildew  ^djpkm  leu*otricka  (E11.  &  Ev.)  Salm.      ....  226 

Root  Rot,  Clitocybe  parasitica  Wilcox 471 

P         f  Gymnosporangium  macropus  Lk 425 

\Gymnosporangium  globos^lm  Farl 426 

Scab,  Venturia  Pomi  (Fr.)  Wint 264 

Sooty  Blotch,  Leptothyrium  Pomi  (Mont.  &  Fr.)  Sacc 367 

Spongy  Dry  Rot,  Volutella  fructi  Stevens  &  Hall 316 

Apricot  (Prunus  Armeniaca  L.) 

Black  Knot,  Plowrightia  morbosa  (Schw.)  Sacc 248 

Brown  Rot,  Sclerotinia  fructigena  (Pers.)  Schroet 187 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     .    .     .  114 

Rust,  Puccinia  Pruni-spinosce  Pers 417 

Scab,  or  Peach  Scab,  Cladosporium  carpophilum  Thiim 299 

Arbor  Vitae  (Thuja  occidentalis  L.) 

Root  Rot,  Polyporus  Schuueinitzii  Fr 463 

Artichoke,  Jerusalem  (Helianthus  tuberosus  L.) 

Mildew,  Plasmopara  Halstedii  Farl 161 

Rust,  Puccinia  Helianthi  Schw 420 

Ash  (Fraxinus  spp.) 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Rot,  Polyporus  Fraxinophilus  Pk 464 

White  Rot,  Polyporus  squamosus  (Huds.)  Fr 453 

Asparagus  (Asparagus  spp.) 

Damping-off,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt  444 

European  Root  Disease,  Rhizoctonia  Medicaginis  De  C 477 

Rust,  Puccinia  Asparagi  De  C 4°3 

Aster  (Aster  spp.) 

Leaf  Blight,  or  Smut,  Entyloma  compositarum  Farl 381 

Rust,  Coleosporium  Solidaginis  (Schw.)  Thiim 435 

Aster,  China  (Callistephus  hortensis  Cass.) 

Root  Rot,  or  Rhizoctonia,  Corticitim  vagtim  B.  &  C.,  var.  Solani  Burt    .  444 

Wilt,  Fusarium  sp 320 

Balsam  (Abies  balsamea  (L.)  Mill.) 

Decay,  Fomes  Pinicola  Fr 467 

Barberry  (Berberis  spp.) 

Puccinia  graminis  Pers 408 

Barley  (Hordeum  spp.) 

Ergot,  Claviceps  purpurea  (Fr.)  Tul 244 

-n          (Puccinia  graminis  Pers 408 

\^Puccinia  rubigo-vera  (De  C.)  Wint 416 

Smut,  Ustilago  nuda  (Jens.)  Kell.  &  Sw 377 


HOST  INDEX  OF  FUNGOUS  DISEASES  485 

Barnyard  Grass  (Echinochloa  crusgalli  (L.)  Beauv.) 

Smut,  Tolyposporium  bullatum  (Schroet.)  Schroet. 378 

Basswood  (Tilia  spp.) 

Anthracnose,  Glceosporium  Ttlice  Oudem 335 

White  Rot,  Polyporus  squamosus  (Huds.)  Fr 453 

Bean  (Phaseolus  vulgaris  L.,  P.  lunatus  L.,  etc.) 

Anthracnose,  Colletotrichum  Lindemuthianum  (Sacc.  &  Magn.)  Bri.  & 

Cav 322 

Blight,  Pseudomonas  Phaseoli  Erw.  Smith 119 

Damping-off,  Pythium  de  Baryanum  Hesse 141 

Downy  Mildew,  Phytophthora  Phaseoli  Thaxter 171 

Powdery  Mildew,  Erysiphe  Polygoni  De  C 227 

Rust,  Uromyces  appendiculatus  (Pers.)  Lev 397 

Stem  Blight,  Root  Rot,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var. 

Solani  Burt •  '•".    /•  •    -  444 

Beech  (Fagus  grandifolia  Ehrb.) 

Decay,  Fames  fomentarius  (L.)  Fr 467 

Heart  Rot,  Fames  igniarius  (L.)  Gillett 465 

Seedling  Disease,  Phytophthora  cactonnn  (Leb.  &  Cohn)  Schroet.     .     .  173 

Beet  (Beta  vulgaris  L.) 

European  Root  Disease,  Rhizoctonia  Medicaginis  De  C 477 

Gall,  Urophlyctis  leproides  (Trabut)  Magn - 140 

Heart  Rot,  Phoma  Beta:  Frank 343 

Leaf  Blight,  Cercospora  Beticola  Sacc 309 

Root  Rot,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt    .  444 

Rust,  Uromyces  Betce  (Pers.)  Kiihn 399 

Scab,  Oospora  scabies  Thaxter 290 

White  "  Rust,"  Cystopus  Bliti  (Biv.)  Lev.    .    .  ;\    .-    .' 152 

Bent  Grass  (Agrostis  spp.) 

Rust,  Puccinia  graminis  Pers.      .    .    .  "*'   .  ' ." '. 408 

Bilberry  ( Vaccinium  Myrtittus  L.) 

Sclerotial  Disease,  Sclerotinia  baccarum  Schroet 195 

Birch  (Betula  sp.) 

Decay,  Fames  fomentarius  (L.)  Fr 467 

Heart  Rot,  Fomes  igniarius  (L.)  Gillett <    .  465 

Sapwood  Decay,  Polyporus  Betulinus  (Bull.)  Fr 464 

Sclerotial  Disease,  Sclerotinia  Betiilce  Wor 201 

Blackberry  (Rubus  spp.) 

Anthracnose,  Glceosporium  Venetum  Speg 334 

C         Bl'   ht  J  Coniothyrium  Fuckelii  Sacc 354 

\Leptosphceria  Coniothyrium  (Fckl.)  Sacc 356 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     ...  114 

Gall,  or  Chytridiose,  Pycnochytrium  globosum  Schroet 139 

Leaf  Spot,  Septoria  Rubi  West 363 

Rust,  Gymnoconia  Peckiana  (Howe)  Tranz 427 


486  HOST  INDEX  DF  FUNGOUS  DISEASES 

PAGE 

Bluegrass  (Poa  spp.) 

f  Claviceps  micracephala  ( Wallr.)  Tul.  .  'V 247 

Ergot  ^  Claviceps  purpurea  (Fr.)  Tul 244 

^Claviceps  setulosa  (Quel.)  Sacc 247 

Rust,  Puccinia  graminis  Pers *.  .'  .  .  408 

Blue-Stem  Grass  (Andropogon  spp.) 

Smut,  Sorosporium  Syntherismce  (Pk.)  Farl. 378 

Bog  Bilberry  (Vaccinium  uliginosum  L.) 

Sclerotial  Disease,  Sclerotinia  heteroica  Won  &  Nawasch.       .     .     ...     .     195 

Borage  (Anchusa  spp.) 

Brown  Rust,  Puccinia  nibigo-vera  (De  C.)  Wint 416 

Brome  Grass  (Bromus  spp.) 

Rust,  Puccinia  graminis  Pers 408 

Buckwheat  (Fagopyrum  esculentum  Moench.) 

False  Mildew,  or  Leaf  Blight,  Ramularia  rufomaculans  Pk 297 

Buttercup  (Ranunculus  spp.) 

Leaf  Spot,  or  Smut,  Entyloma  Ranunculi  (Lion.)  Schroet 381 

Butternut  (Juglans  cinerea  L.) 

Anthracnose,  Glceosporium  Juglandis  (Lib.)  Mont. 335 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Cabbage,  Cauliflower,  etc.  (Brassica  oleracea  L.) 

Black  Rot,  Pseudomonas  campestris  (Pammel)  Erw.  Smith 107 

Club  Root,  Plasmodiophora  Brassicce  Wor */..  .  \    .  97 

Downy  Mildew,  Peronospora  parasitica  (Pers.)  De  Bary 161 

Root  Rot  or   Stem   Rot,   Rhizoctonia,  Corticium   vagum  B.  &  C.,  var. 

Solani  Burt 444 

Soft  Rot,  Bacillus  carotovorus  Jones 131 

White  Rust,  Cystopus  candidus  (Pers.)  Lev 149 

Calla  (Zantedeschia  (Ethiopica  (L.)  Spreng.) 

Soft  Rot,  Bacillus  aroideee  Townsend 133 

Canada  Thistle  (Cirsium  arvense  (L.)  Scop.) 

Rust,  Puccinia  suaveolens  (Pers.)  Rostr 421 

Carnation  (Dianthus  Caryophyllus  L.) 

Anthracnose,  Volutella  Dianthi  Atkinson 317 

Bud  Rot,  Sporotrichum  Poce  Pk •;--:'.  vC:    .  293 

Leaf  Spot,  Septoria  Dianthi  Desm 363 

Root  Rot,  or*  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt    .  444 

Rust,  Uromyces  Caryophyllinus  (Schrank)  Wint 399 

Wilt,  Fusarium  sp ".    ...  321 

Carrot  (Daucus  Carota  L.) 

Root  Rot,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt     .    444 
Soft  Rot,  Bacillus  carotovorus  Jones 131 

Catalpa  (Catalpa  Bignonioides  Walt.) 

Leaf  Blight,  Macrosporium  Catalpa  Ell.  &  Mart 347 

Leaf  Spot,  Phyllosticta  Catalpce  Ell.  &  Mart 347 


HOST  INDEX  OF  FUNGOUS  DISEASES  487 

Cauliflower.   See  Cabbage.  PAGE 

Cedar,  Red  (Juniperus  spp.) 

Feckiness,  or  Red  Rot,  Polyporus  carneus  Nees 463 

(Gymnosporangiumglobosum  Farl 426 

Rust  \  Gymnosporangium   macropus   Lk 425 

\^Gymnosporangium  Sabince  Plowr 426 

White  Rot,  Polyporus  Juniperinus  von  Schrenk 463 

Celery  (Apium  graveolens  L.) 

Damping-off,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt  444 

Early  Leaf  Blight,  Cercospora  Apii  Fr 312 

Late  Blight,  Septoria  Petroselini  Desm.,  var.  Apii  Br.  &  Cav.    ,    .     .    .  361 

Chard  (Beta  cycla  L.) 

Leaf  Spot,  Cercospora  Beticola  Sacc 309 

Chenopodiacese 

Leaf  Gall,  Urophlyctis  pulposa  (Wall.)  Schroet 140 

Cherry  (Prunus  spp.) 

Black  Knot,  Plowrightia  morbosa  (Schw.)  Sacc 248 

Brown  Rot,  or  Fruit  Mold,  Sclerotinia  fructigena  (Pers.)  Schroet.   .    .     .  187 

Crown  Gall, Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     ...  114 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Leaf  Curl  and  Witches'  Broom,  Exoascus  Cerasi  Fuckel 185 

Leaf  Spot  (cylindr^porium  /W*  Karst 339 

\Mycosphcerella  Cerasella  Aderh 263 

Powdery  Mildew,  Podosphara  Oxyacantha  (De  C.)  De  Bary 226 

Root  Rot  (Armillar^~  mellea  Vahl 473 

\Clitocybe  parasitica  Wilcox 471 

Rust,  Puccin ia  Pruni-spinosce  Pers 417 

Scab,  Cladosporium  carpophilum  Thiim 299 

Shot  Hole,  Cercospora  circumscissa  Sacc 314 

Chestnut  (Castanea  spp.) 

Bark  Disease,  or  Canker,  Diaporthe parasiticq  Murrill 281 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Leaf  Spot,  or  Anthracnose,  Marsonia  ochroleuca  B.  &  C 336 

Chrysanthemum  (Chrysanthemum  spp.) 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Leaf  Blight,  Cylindrosporium  Chrysanthemi  Ell.  &  Dearn 343 

Leaf  Spot,  Septoria  Chrysanthemi  Cav 364 

Rust,  Puccinia  Chrysanthemi  Roze 421 

Clover  (Trifolium  spp.) 

Anthracnose,  Colletotrichum  Trifolii  Bain 328 

Damping-off,  Pythium  de  Baryanum  Hesse 141 

Leaf  Spot,  Pseudopeziza  Trifolii  (Pers.)  Fckl 204 

Rust,  Uromyces  Trifolii  (Hedw.)  Lev 395 

Sooty  Spot,  Polythrincium  Trifolii  Kze 298 

Stem  Rot,  Sclerotinia  Trifoliorum  Eriks 201 


488  HOST  INDEX  OF  FUNGOUS  DISEASES 

Cocklebur  (Xanthium  spp.)  PAGE 

Rust,  Puccinia  Xanthii  Schw 393 

Coffee  (Coffea  arabica  L.) 

Rust,  Hemileia  vastatrix  Berk.  &  Br 393 

Cordyline  (Cordyline  spp.) 

Leaf  Spot,  Phyllosticta  maculicola  Hals 347 

Corn  (Zea  mays  L.) 
Blight.   See  Wilt. 

Damping-off,  Pythium  de  Baryanum  Hesse 141 

Downy  Mildew,  Sclerospora  macrospora  Sacc 'I    .    ''.'"'  .  161 

Rust,  Puccinia  Sorghi  Schw 414 

Smut  [Ustilago  Ze<e  (T&tx&xn.}  Ung.    .    ..:.*,    ....,_...,..„-.-.,.  376 

\^Ustilago  Reiliana  Kiihn 377 

Wilt,  Pseudomonas  Stewarti  Erw.  Smith 1 1 1 

Cotton  (Gossypium  spp.) 

Angular  Leaf  Spot,  Pseudomonas  malvacearum  Erw.  Smith 121 

Anthracnose,  Colletotrichum  Gossypii  Southworth 325 

Black  "Rust,"  Macrosporium  nigricantium  Atk.       ....    .    .    ..."    .  304 

Damping-off,  Sore  Skin,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var. 

Solani  Burt        444 

False  or  Areolate  Mildew,  Ramularia  areola  Atk 296 

Leaf  Spot,or  Blight  <C*™>*P<™  Gossypina  Cke.    .  Y  ,-  .    ;.  .-   .  -,      .  313 

\JSphcerella  Gossypina  Atk 313 

Root  Rot,  Ozonium  omnivorum  Shear 479 

Wilt,  or  Frenching,  Neocosmospora  vasinfecta  (Atk.)  Erw.  Smith    .    .     .  233 

Couch  grass  (Agropyron  repens  (L.)  Beauv.) 

Rust,  Pticcinia  graminis  Pers 408 

Cowberry  (Vaccinum  Vitis-Id&a  L.) 

Gall,  Exobasidium  Vaccinii  (Fckl.)  Wor **.    .'    .  440 

Sclerotial  Disease,  Sclerotinia  Vaccinii  Wor 195 

Crab  grass  (Panicum  sanguinale  L.) 

Leaf  Spot,  or  Blast,  Piricularia  grisea  (Cke.)  Sacc 297 

Cranberry  (Vaccinium  spp.) 

Gall,  Exobasidium   Vaccinii  (Fckl.)  Wor 440 

Gall,  or  Chytridiose,  Synchytrium  Vaccinii  Thomas 138 

Scald,  Guignardia  Vaccinii  Shear 259 

Sclerotial  Disease,  Sclerotinia  Oxycocci  Wor 195 

Spot,  Pestalozzia  Guepini  Desm.,  var.  Vaccinii  Shear 338 

Cress  (Lepidium  sativum  L.) 

Damping-off,  Pythittm  de  Baryanum  Hesse 141 

Crowberry  (Empetrum  nigrum  L.) 

Sclerotial  Disease,  Sclerotinia  megalospora  Wor 195 


HOST  INDEX  OF  FUNGOUS  DISEASES  489 

Cucumber  (Cucumis  sativus  L.)  PAGE 

Anthracnose,  Colletotrichum  Lagenarium  (Pass.)  Ell.  &  Hals 330 

Blight,  or  Wilt,  Bacillus  tracheiphilus  Erw.  Smith 129 

Damping-off,  Pythiiim  de  Baryanum  Hesse 141 

Downy  Mildew,  Plasmopara  cubensis  (B.  &  C.)  Humphrey 158 

Powdery  Mildew,  Erysiphe  Cichoracearum  De  C 228 

Scab,  Cladosporium  Cucumerinum  Ell.  &  Arth 300 

Stem  Rot,  Sclerotinia  Libertiana  Fckl 198 

Wilt.    See  Blight. 

Currant  (Ribes  spp.) 

Anthracnose,  Pseudopeziza  Ribis  Kleb 204 

Cane  Blight,  Nectria  cinnabarina  (Tode)  Fr 239 

Cane  Wilt,  Dothiorella 364 

Leaf  Spot,  Septoria  Ribis  Desm 362 

Powdery  Mildew,  Spharotheca  Mors-uv<?  (Schw.)  B.  &  C 221 

f Cronartium  Ribicola  Fisch.  de  Waldh .'".,„...'  :'.    .  433 

Rust  -|  ^Ecidium  Grossularice  Schum 393 

^Puccinia  Ribis  De  C _.-,.'..••./.''•'•'    .*.'..  393 

Dracaena  (Drac&na  spp.) 

Leaf  Spot,  Phyllosticta  maculicola  Hals 347 

Eggplant  (Solanum  Melongena  L.) 

Blight,  Bacillus  solanacearum  Erw.  Smith 134 

Leaf  Spot,  Phyllosticta  hortorum  Speg 346 

Seedling  Stem  Blight,  Phoma  Solani  Hals 345 

Elm  (Ulmus  spp.) 

Blister  Canker,  Nummularia  discreta  Tul.  , 282 

White  Rot,  Polyporus  squamosus  (Huds.)  Fr 453 

Evening  Primrose  ((Enothera  biennis  L.) 

Gall,  or  Chytridiose,  Synchytrium  fulgens  Schroet. 139 

Fig  (Ficus  Carica  L.) 

Rust,  Uredo  Fid  Cast 393 

Fir  (Abies  spp.) 

Rust,  ,/Ecidiuni  elatinum  Alb.  &  Schw 393 

Flax  (Linum  spp.) 

Wilt,  Fusarium  Lini  Bolley 319 

Fleabane  (Erigeron  spp.) 

Leaf  Blight,  or  Smut,  Entyloma  compos itarum  Farl 381 

Foxtail  (Setaria  spp.) 

Mildew,  Sclerospora  graminicola  (Sacc.)  Schroet 161 

Ginseng  (Panax  quinquefolium  L.) 

Blight,  Alternaria  Panax  Whetzel 305 

Wilt,  Fusarium  sp 320 


490  HOST  INDEX  OF  FUNGOUS  DISEASES 

Golden-rod  (Solidago  spp.)  PAGE 

Red  Rust,  Coleosporium  Solidaginis  (Schw.)  Thiim 435 

Rust,  Uromyces  Solidaginis  (Somm.)  Niessl 402 

Gooseberry  (Ribes  Grossularia  L.) 

Leaf  Spot,  Septoria  Ribis  Desm 363 

Powdery  Mildew,  Sphcerotheca  Mors-uvtz  (Schw.)  B.  &  C 221 

^          (ALcidium  Grossularice  Schum 393 

\Puccinia  Ribis  De  C 393 

Grape  (JWsspp.) 

Anthracnose,  Glceosporium  ampelophagum  Sacc 332 

Black  Rot,  Guignardia  Bidwellii  (Ell.)  Viala  &  Ravaz 254 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     .    .     .  114 

Downy  Mildew,  Plasmopara  Viticola  (B.  &  C.)  Berl.  &  De  Toni     ...  152 

Leaf  Blight,  Ccrcospora  Viticola  (Ces.)  Sacc 314 

Powdery  Mildew,  Uncinula  necator  (Schw.)  Burr •  .  •,  t    •*  •    •  229 

Ripe  Rot,  or  Anthracnose,  Glomerella  rufomaculans  (Berk.)  Spauld.  & 

von  Schrenk '.,-••  "•    •  271 

Root  Rot  J^"»'""«™  *<"«*  VahL    .    .    .    /.,..?./..    .    .  473 

\Dematophora  necatrix  Hartig 321 

Grape  Fruit  (Citrus  Decumana  Lour.) 

See  Orange. 

Ground  Cherry  (Physalis  pubescens  L.) 

Smut,  Entyloma  Physalidis  (Kalchbr.  &  Cke.)  Wint.  .    ......    .    .    380 

Groundsel  (Senecio  spp.) 

Downy  Mildew,  Bremia  Lactucce  Reg 164 

Hawkweed  (Hieracium  spp.) 

Rust,  Puccinia  Hieracii  (Schum.)  Mart 422 

Hawthorn  (Cratagus  spp.) 

Blight,  Bacillus  amylovorus  (Burr.)  De  Toni 121 

Rust,  Gymnosporangium  clavariceforme  (Jacq.)  Rees 426 

Hepatica  (Hepatica  acutiloba  De  C.) 

Rust,  Puccinia  Pruni-spino see  Pers 417 

Hemlock  (Tsuga  canadensis  (L.)  Carr) 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Dry  Rot,  Trametes  Pini  (Brot.)  Fr 467 

Hickory  (Gary a  alba  (L.)  Koch) 

Root  Rot,  Clitocybe  parasitica  Wilcox 471 

Hog  Peanut  (Amphicarpa  monoica  (L.)  Ell.) 

Gall,  or  Chytridiose,  Synchytrium  decipiens  Farl 139 

Hollyhock  (Alth&a  rosea  Cav.) 

Rust,  Puccinia  malvaceanim  Mont 419 


HOST  INDEX  OF  FUNGOUS  DISEASES  491 

Hop  Hornbeam  (Ostrya  virginiana  (Mill.)  Koch) 

Root  Rot,  Armillaria  mellea  Vahl    .......     .     .    ......    473 

Horse-chestnut  (AZsculus  Hippocastanum  L.) 

Leaf  Blotch,  Phyllosticta  Pavice  Desm  ..............    345 

Horse  radish  (Cochlearia  Armoracia  L.) 

Brown  Spot,  Altemaria  Brassicce  (Berk.)  Sacc  ...........  308 

Root  Rot,    Thielavia  basicola  (B.  &  Br.)  Zopf      ..........  210 

White  "  Rust,"  Cystopus  candidus  (Pers.)  Lev  ...........  149 

Huckleberry  (Gaylussacia,  Vacdnium,  etc.) 

Gall,  Exobasidium  Vaccinii  (Fckl.)  Wor.     .     .     ..........    440 

Hyacinth  (Hyacinthus  orientalis  L.) 

Bacteriosis,  Bacillus  Hyacinthi-septicus  Heinz     ..........     134 

Yellow  Disease,   Pseudomonas  Hyacinthi  (Wakker)  Erw.  Smith     ...     120 

Juniper  (Juniperus  communis  L.) 

Rust,  Gymnosporangitim  clavaricrforme  (Jacq.)  Rees    ........    426 

Knotweed  (Polygonum  spp.) 

Rust,  Puccinia  Polygoni  Pers  .....     ............    393 

Larch  (Larix  decidua  Mill) 

Canker,  Dasyscypha  Willkommii  Hartig  .............  202 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr  ........  457 

Dry  Rot,  Trametes  Pini  (Brot.)  Fr  .............     .     .  467 

Root  Rot,  Polyporus  Schweinitzii  Fr  ...............  463 

Lemon  (Citrus  Medico  var.  Limon  L.) 

Brown  Rot,  Pythiacystis  Citrophthora  R.  E.  Smith  ......    .     .     .     144 

Sooty  Mold.    See  Orange. 

Lettuce  (Lactuca  sativa  L.) 

Damping-off,  or  Rhizoctonia,  Coriicium  vagum  B.  &  C.,  vo.v.Solani  Burt  444 

Downy  Mildew,  Bremia  Lactuca:  Reg  ..............  164 

(Sclerotinia  Libertiana  Fckl  .....     .     .     .     .    .    -."•".    .     .     .  198 


-p 

\Sclerotinia  Fuckeliana  De  Bary 


Leaf  Spot,  Septoria  consimilis  E.  &  M 
Rot.    See  Drop  and  Damping-off. 

Lilac  (Syringa  vulgaris  L.) 

Powdery  Mildew,  Microsphcera  Alni  (Wallr.)  Wint.      .    .......     228 

Lily  (Liliwn  spp.) 

Botrytis,  or  Ward's  Disease,  Sclerotinia  Fuckeliana  De  Bary  .     .         .    .     196 

Locust,  Common  (Robinia  Pseudo-Acacia  L.) 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr.  .          .....    457 

Magnolia  (Magnolia  grandiflora] 

Leaf  Spot,  Phyllosticta  Magnolia  Sacc  ..............    347 

Mallow  (MalvacetR) 

Rust,  Puccinia  malvacearum  Mont  ........    ,     ......    4I9 


492 


HOST  INDEX  OF  FUNGOUS  DISEASES 


Maple  (Acer  spp.) 

Anthracnose,  Glaosporium  apocryptum  E.  &  E 335 

Decay,  Fomes  fomentarius  (L.)  Fr 467 

Gall,  or  Chytridiose,  Pycnochytrium  globosum  Schroet 139 

Heart  Rot  [Fomes  ^gniarius  (L.)  Gillett     .    .    .    .   •;'•  v  :^ 465 

\Hydnum  septentrionale  Fr 452 

Leaf  Blotch,  or  Black  Spot,  Rhytisma  Acerinum  (Pers.)  Fr 208 

Powdery  Mildew,  Uncinula  Aceris  (De  C.)  Wint 231 

White  Rot,  Polyporus  squamosus  (Huds.)  Fr 453 

Meadow  Foxtail  (Alopecurus  pratensis  L.) 

Rust,  Puccinia  graminis  Pers 408 

Mints  (Labiate) 

Rust,  Puccinia  Menthce  Pers.    . 407 

Morning  Glory  (Convolvulac&e) 

White  "Rust,"  Cystopus  convolvulacearum  Otth 152 

Mountain  Ash  (Pyrus  Aucuparia  (L.)  Ehrb.) 

Rust,  Gymno sporangium  globosum  Farl 426 

Sclerotial  Disease,  Sclerotinia  Aucuparia  Ledw 195 

Mulberry  (Moms  sp.) 

Blight,  Bacillus  Cubonianus  Macch 134 

Muskmelon  (Cucumis  Melo  L.) 

Anthracnose,  Blight,  Downy  Mildew,  Leaf  Spot,  Wilt.    See  Cucumber. 

Mold,  Cladosporium  Cucumerinum  Ell.  &  Arth 300 

Mustard  (Brassica  spp.) 

Black  Rot,  Psetidomonas  campestris  (Pammel)  Erw.  Smith 107 

Club  Root,  Plasmodiophora  Brassicce  Wor 97 

White  "  Rust,"  Cystopus  candidus  (Pers.)  Lev 149 

Oak  (Quercus  spp.) 

Anthracnose,  Gnomonia  Veneta  (Sacc.  &  Speg.)  Kleb 278 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Heart  Rot,  Fomes  igniarius  (L.)  Gillett 465 

(Rosellinia  Quercina  Hartig 280 

Root  Rot  •*>  Clitocybe parasitica  Wilcox 471 

^Armillaria  mellea  Vahl 473 

White  Rot,  Polyporus  sqttamosiis  (Huds.)  Fr 453 

Oats  (Avena  sativa  L.) 

(Puccinia  coronata  Cda 420 

Rust  \  Puccinia  graminis  Pers ;.  -.r  ;  .  .  .  408 

'^Puccinia  rubigo-vera  (De  C.)  Wint 416 

Smut  (UstilaS°  Avena  (Pers.)  Jens 372 

\Ustilago  levis  (Kell.  &  Sw.)  Magn 373 

Okra  (Hibiscus  esculentus  L.) 

Wilt,  or  Frenching,  Neocosmospora  vasinfecta  (Atkinson)  Erw.  Smith     .  233 


HOST  INDEX  OF  FUNGOUS  DISEASES  493 

Oleander  (Nerium  Oleander  L.)  PAGE 


Tubercle  Disease  (Arc.)  Trev.     .     .    ......  118 

{^Pseudomonas  tumefaciens  Smith  &  Townsend  .     .    .  114 

Olive  (Olea  europ&a  L.) 

Tubercle  Disease,  Pseudomonas  Ole<z  (Arc.)  Trev  .........  118 

Onion  (Allium  Cepa  L.) 

Downy  Mildew,  Peronospora  Schleideniana  De  Bary    ........  i6z 

Mold,  Macrosporium  Sarcinula  Berk.,  van  parasiticum  Thiim  .....  304 

Rust,  Puccinia  Allii  De  C  ...................  393 

Smut,  Urocystis  Cepulce  Frost  .................  381 

Orange  (Citrus  Aurantium  L.,  and  C.  nobilis  Lour.) 

Brown  Rot,  Pythiacystis  Citrophthora  R.  E.  Smith  .........  144 

Sooty  Mold,  Meliola  Camellia  (Catt.)  Sacc  ............  213 

Wither  Tip,  Colletotrichum  Glceosporioides  Penz  ..........  327 

Orchard  Grass  (Dactylis  glomerata  L.) 

TJ          (Puccinia  coronata  Cda  .................  420 

\JPucciniagraminis  Pers  .................  408 

Oxalis  (Oxalis  spp.) 

Rust,  Piiccinia  Sorghi  Schw  ..................  414 

Parsnip  (Pastinaca  sativa  L.) 

Early  Blight,  Cercospora  Apii  Fr  ................  312 

Pea  (Pisum  spp.) 

Powdery  Mildew,  Erysiphe  Polygoni  De  C  ............  227 

Root  Rot,  Thielavia  basicola  (B.  &  Br.)  Zopf     ..........  210 

Rust,  Uromyces  Pisi  (Pers.)  De  Bary    ..............  398 

Stem  Rot,  or  Root  Rot,  Corticium  vagum  B.  &  C.,  van  Solani  Burt    .    .  444 

Peach  (Prunus  Persica  Benth.  &  Hook.) 

Anthracnose,  Glceosporium  Itzticolor  Berk  .............  335 

Blight,  Coryneum  Beijerinckii  Oudem.     .    .     .    1    .........  336 

Brown  Rot,  Sclerotinia  friictigena  (Pers.)  Schroet  ..........  187 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend     ...  114 

Frosty  Mildew,  or  False  Mildew,  Cercosporella  Persicce  Sacc  ......  297 

Leaf  Curl,  Exoascus  deformans  (Berk.)  Fuckel    ..........  176 

Powdery  Mildew  [Sph^rotheca  pannosa  (Wallr.)  Lev  ........  224 

\^Podosphcera  Oxyacanthce  (De  C.)  De  Bary      ....  226 

Root  Rot,  Clitocybe  parasitica  Wilcox       .............  471 

Rust,  Puccinia  Pruni-spinosce  Pers  ...............  417 

Scab,  Cladosporium  carpophilum  Thiim  ..............  299 

Pear  (Pyrus  communis  L.) 

Blight,  or  Fire  Blight     1    „     .,,  /*>•''%  T^  >•»• 

w  Bacillus  amylovorus  (Burr.)  De  Tom  .    .    .    .  121 
Body  Blight,  or  Canker/ 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend.     .    .     .  114 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr  ........  457 

Leaf  Blight,  Entomosporium  maculatum  Lev  .....    ,,,...  365 


494 


HOST  INDEX  OF  FUNGOUS   DISEASES 


Pear  (Pyrus  communis  L.)  (Continued) 

Leaf  Spot,  Septoria  Pyricola  Desm 358 

["  Gymno sporangium  clavariceforme  (Jacq.)  Rees 426 

Rust  4.  Gymnosporangium  globosum  Farl 426 

\^Gymnosporangium  Sabince  Plowr 426 

Scab,  Venturia  Pyrina  Aderh 264 

Pepper  (Capsicum  annuum  L.) 

Anthracnose,  Colletotrichum  nigrum  Ell.  &  Halsted 330 

Persimmon  (Diospyros  virginiana  L.) 

Leaf  Blight,  Cercospora  Diospyri  Thiim 315 

Pigweed  (Amarantaces.  spp.) 

White  "  Rust,"  Cystopus  Bliti  (Biv.)  Lev 152 

Pine  (Pinus  spp.) 

Blight,  Pestalozzia  Hartigii  Tub 339 

D      R   t  $F°mes  Pinicola  Fr 467 

\Trametes  Pint  (Brot.)  Fr 467 

Root  Rot,  Polyporus  Schweinitzii  Fr 463 

.p          f  Coleosporium  Solidaginis   (Schw.)  Thiim 435 

\Cronartium  Ribicola  Fisch.  de  Waldh. 433 

Plum  (Prunus  spp.) 

Black  Knot,  Plowrightia  morbosa  (Schw.)  Sacc 248 

Blight,  Bacillus  amylovorus  (Burr.)  De  Toni 121 

Brown  Rot,  or  Fruit  Mold,  Sclerotinia  fructigena  (Pers.)  Schroet.   .    .    .  187 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Leaf  Spot,  Cylindrosporium  Padi  Karst 339 

Plum  Pockets,  Exoascus  Pruni  Fuckel 183 

Powdery  Mildew,  Podosphcera  Oxyacanthce  (De  C.)  De  Bary 226 

Root  Rot,  Arniillaria  mellea  Vahl 473 

Rust,  Puccin ia  Pruni-spinos<z  Pers 417 

Scab,  Cladosporium  carpophilum  Thiim 299 

Poplar  (Populus  spp.) 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  -Smith  &  Townsend      ...  114 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr 457 

Heart  Rot,  Fames  igniarius  (L.)  Gillett 465 

Leaf  Spot,  or  Anthracnose,  Marsonia  Populi  (Lib.)  Sacc 336 

Powdery  Mildew,  Uncinula  Salicis  (De  C.)  Wint 230 

Rust,  Melampsora  tremula;  Tul 437 

Poverty  Grass  (Aristida  spp.) 

Smut,  Sorosporiiim  Syntherismtz   (Pk.)  Farl 378 

Potato  (Solatium  tuberosum  L.) 

Blight,  Bacillus  solanacearum  Erw.  Smith 134 

Downy  Mildew,  or  Dry  Rot  of  Tubers,  Phytophthora  infestans  (Mont.) 

De  Bary 165 

Dry  Rot,  or  Stem  Blight,  Fusarium  oxysporum  Schl 317 

Early  Blight,  Macrosporium  Solani  E.  &  M 301 

Rhizoctonia,  or  Scurf,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt .    .    .  444 

Scab,  Oospora  scabies  Thaxter  .,..,,,,,,,.,,.,,  290 


HOST  INDEX  OF  FUNGOUS  DISEASES 


495 


Privet  (Ligustrum  vulgare  L.)  PAGE 

Anthracnose,  Glceosporium  cingulatum  Atkinson 335 

Pumpkin.    See  Squash. 

Quince  (Cydonia  vulgaris  Pers.) 

Bitter  Rot,  Glomerella  rufomaculans  (Berk.)  Spauld.  &  von  Schrenk  .     .  271 

Black  Rot,  Sphteropsis  Malorum  Pk 350 

Blight,  or  Fire  Blight,  Bacillus  amylovonis  (Burr.)  De  Toni 121 

Leaf  Blight,  or  Fruit  Spot,  Entomosporium  maculatum  Lev 365 

Rust,  Gyrnno sporangium  globosum  Farl 426 

Radish  (Raphanus  sativus  L.) 

Club  Root,  Plasmodiophora  Brassicce  Wor 97 

Damping-off,  or  Rhizoctonia,  Corticium  vagum  B.  &.  C.,  var.  Solani  Burt  444 

Damping-off,  Pythium  de  Baryanum  Hesse 141 

Downy  Mildew,  Peronospora  parasitica  Pers 161 

White  "  Rust,"  Cystopus  candidus  (Pers.)  Lev 149 

Raspberry  (Rubus  spp.) 

Diseases.    See  Blackberry. 

Rhododendron  (Rhododendron  spp.) 

Rust,  Chrysomyxa  Rhododendri  (De  C.)  De  Bary 432 

Sclerotial  Disease,  Sclerotinia  Rhododendri  Fischer 196 

Rice  (Oryza  sativa  L.) 

Blast,  Plricularia  grisea  (Cke.)  Sacc 297 

Smut,  Tilletia  horrida  Tak 380 

Rice,  Wild  (Leersia  spp.) 

Smut,  Tilletia  corona  Scrib „  380 

Rose  (Rosa  spp.) 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Downy  Mildew,  Peronospora  sparsa  Berk 164 

Leaf  Blotch,  Actinonema  Rosa  (Lib.)  Fr.      .    . 357 

Powdery  Mildew,  Spharotheca pannosa  (Wallr.)  Lev 224 

Rust,  Phragmiditim  subcorticium  (Schrank)  Winf. 430 

Rye  (Secale  cereale  L.) 

Ergot,  Claviceps  purpurea  (Fr.)  Tul 244 

Powdery  Mildew,  Erysiphe  graminis  De  C 217 

^         [Puccinia  graminis  Pers 408 

\^Puccinia  rubigo-vera  (De  C.)  Wint 416 

Smut,  Urocystis  occulta  (Wallr.)  Reb 383 

Salsify  ( Tragopogon  porrifolius  L.) 

Rust,  Puccinia  Tragopogi  (Pers.)  Cda 421 

White  "  Rust,"  Cystopus  Tragopogonis  Pers 152 

Shepherd's  Purse  (Capsella  Bursa-pastoris) 

Club  Root,  Plasmodiophora  Brassicce  Wor 97 

Downy  Mildew,  Peronospora  parasitica  (Pers.)  De  Bary 161 

White  "  Rust,"  Cystopus  candidus  Lev 149 


496  HOST  INDEX  OF  FUNGOUS  DISEASES 

Snapdragon  (Antirrhinum  majus  L.)  PAGE 

Anthracnose,  Colletotrichum  Antirrhini  Stewart      .........    329 

Sorghum  (Sorghum  spp.) 

Rust,  Puccinia  Sorghi  Schw  ..........  '   ........    414 

Smut,  Ustilago  Reiliana  Kiihn      ................    377 

Sorrel  (Rumex  spp.) 

Rust,  Uromyces  Rumicis  (Schum.)  Wint.       .    .    .    .  °  ........    402 

Spinach  (Spinacia  oleracea  Mill.) 

Downy  Mildew,  Peronospora  effusa  (Grev.)  Rabh  ..........     164 

Spruce  (Picea  spp.) 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr  ........    457 


Drv  Rot  $Fomes  Pi™ola  Fr  ..................    467 

\Trametes  /i>*/  (Brot.)  Fr  ...............    467 


Root  Rot  (PolyP°rus  borealis  (  Wahl.)  Fr  .............  463 

\Polyporus  Schweinitzii  Fr  ..............  463 

Rust,  Chrysomyxa  Rhododendri  (De  C.)  De  Bary     .........  432 

Spurge  (Euphorbia  spp.) 

R     t  [Uromyces  Pisi  (Pers.)  De  Bary       .............  398 

\^Uromyces  scutellatus  (Schr.)  Wint  .............  402 

Squash  (Cucurbita  spp.) 

Anthracnose,  Blight  or  Bacterial  Wilt,  Downy  Mildew,  Fruit  Mold,  Pow- 

dery Mildew.    See  Cucumber. 

Root  Rot,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt    .  444 

Star  Cucumber  (Sicyos  angulatus  L.) 

Downy  Mildew,  Plasmopara  cubensis  (B.  &  C.)  Humphrey  ......  158 

Strawberry  (Fragaria  spp.) 

Gall,  or  Chytridiose,  Pycnochytrium  globosum  (Schroet.)  Schroet.  .    .    .  139 

Leaf  Spot,  Mycosphcerella  Fragarice  (Tul.)  Lindau    .........  261 

Powdery  Mildew,  Sphcerotheca  Humuli  De  C  ...........  226 

Sugar  Cane  (Saccharum  officinarum  L.) 

Bundle  Blight,  Pseudomonas  vascularum  (Cobb)  Erw.  Smith  .....  120 

Leaf-splitting  Blight,  Mycosphcerella  stratiformans  Cobb      ......  263 

Red  Rot,  Colletotrichum  falcatum  Sacc  ........    ........  330 

Root  Disease  [Marasmius  plicatus  V&bsx    .....   ....-.;-..    .  469 

\Marasmius  Sacchan  Wakker  ...........  469 

Sunflower  (Helianthus  annuus  L.) 

Damping-off,  Pythium  de  Baryanum  Hesse    ...........  141 

Downy  Mildew,  Plasmopara  Halstedii  Farl  ............  161 

Rust,  Puccinia  Helianthi  Schw  .................  42° 

Sweet  Potato  (Ipomoea  Batatas  Lam.) 

Black  Rot,  Spharonema  fimbriatum  (Ell.  &  Hals.)  Sacc.  .    .    .    ,:  .    .    .  348 

Dry  Rot,  Phoma  Batata  Ell.  &  Hals.    .     .............  344 

Root  Rot,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt     .  444 


HOST  INDEX  OF  FUNGOUS  DISEASES  497 

Sweet  Potato  (Ipomcea  Batatas  Lam.)  (Continued]  PAGE 

Root  Rot,  Ozonium  omnivorum  Shear  • 479 

Soft  Rot,  Rhizopus  nigricans  Ehr : 349 

Stem  Rot,  Nectria  Ipomcea  Hals 243 

White  "  Rust,"  Cystopus  convolvulacearum  Otth 152 

Sycamore  (Platanus  occidentalis  L.) 

Anthracnose,  Gnomonia  Veneta  (Sacc.  &  Speg.)  Kleb 278 

Teosinte  (Euchl&na  luxurious  Dur.  &  Asch.) 

Smut,  Ustilago  Zece  (Beckm.)  Ung 376 

Timothy  (Phleum  pratense  L.) 

Ergot,  Claviceps  purpurea  (Fr.)  Tul 244 

Rust,  Puccinia  Phlei-pratensis  Eriks.  &  Henn 415 

Tobacco  (Nicotiana  Tabacum  L.) 

Damping-off,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt.  444 

Leaf  Spot,  Cercospora  Nicotiance  E.  &  E 31  c 

Powdery  Mildew,  Erysiphe  Cichoracearuni  De  C 228 

Root  Rot,  Thielavia  basicola  (B.  &  Br.)  Zopf 210 

White  Spot,  Macrosporium  Tabacimim  Ell.  &  Ev 304 

Wilt,  or  Granville  Wilt,  Bacillus  solanacearum  Erw.  Smith 134 

Tomato  (Lycopersicwn  esculentum  Mill.) 

Anthracnose,  Colletotrichum  Phomoides  (Sacc.)  Chester 330 

Blight,  Bacillus  solanacearum  Erw.  Smith 134 

Downy  Mildew,  Phytophthora  infestans  (Mont.)  De  Bary 165 

Fruit  Rot,  Macrosporium  Solani  E.  &  M 301 

Leaf  Mold,  Cladosporium  fulvum  Cke 300 

Leaf  Spot,  Septoria  Lycopersici  Speg 362 

Rot  (cause  variously  determined). 

Stem  Rot,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt 444 

Sleepy  Disease,  or  Wilt,  Fusarium  Lycopersici  Sacc 318 

Trumpet  Creeper  (Tecoma  radicans  (L.)  Juss.) 

Leaf  Blight,  Cercospora  sordida  Sacc 315 

Turnip  (Brassica  campestris  L.,  and  B.  Rapa) 

Black  Rot,  Pseudomonas  campestris  (Pammel)  Erw.  Smith 107 

Club  Root,  Plasmodiophora  Brassica  Wor 97 

Downy  Mildew,  Peronospora parasitica  (Pers.)  De  Bary 161 

Powdery  Mildew,  Erysiphe  Polygoni  De  C 227 

White  "  Rust,"  Cystopus  candidus  (Pers.)  Lev 149 

Verbena  (Verbena  spp.) 

Powdery  Mildew,  Erysiphe  Cichoracearum  De  C 228 

Vetch  (View  spp.) 

Powdery  Mildew,  Erysiphe  Polygoni  De  C ,     .     .     .     „  227 

Rust,  Uromyces  Pisi  (Pers.)  De  Bary 398 


498  HOST  INDEX  OF  FUNGOUS  DISEASES 

Violet  (Viola  spp.)  PAGE 

Gall,  or  Chytridiose,  Pycnochytrittm  globosum  (Schroet.)  Schroet.  .    .    .     139 
Leaf  Blight,  Cercospora  Viola  Sacc  ...............    315 


L    f  S  ot  [Alternaria  Viola  Gall.  &  Dorsett  ...........  308 

\Phyllosticta  Violce  Desm  .............     .     .  347 

Root  Rot,  Thielavia  basicola  (B.  &  Br.)  Zopf       ..........  210 

Rust,  Puccinia  Violce  (Schum.)  De  C  ...............  407 

Walnut  (Juglans  spp.) 

Blight,  Pseudomonas  Juglandis  Pierce  ..............  120 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Tovvnsend      ...  1  14 

Decay,  Polyporus  sulphureus  (Bull.)  Fr.  .    .    ...........  457 

Water  Cress  (Radicula  Nasturtium-aquaticum  (L.)  Britten  &  Rendle) 

White  "  Rust,"  Cystopus  candidus  (Pers.)  Lev  ...........  149 

Watermelon  (Citrullus  vulgaris  Schrad.) 

Anthracnose,  Downy  Mildew,  Leaf  Mold,  Leaf  Spot.    See  Cucumber. 

Damping-off,  or  Rhizoctonia,  Corticium  vagum  B.  &  C.,  var.  Solani  Burt  444 

Wilt,  Neocosmospora  vasinfecta  (Atkinson)  Erw.  Smith    .......  233 

Wheat  (Triticum  spp.) 

Ergot,  Claviceps  purpurea  (Fr.)  Tul  ...............  244 

(Puccinia  coronata  Cda  .................  420 

Rust  <j  Puccinia  graminis  Pers  .................  408 

^Puccinia  rubigo-vera  (De  C.)  Wint  ......    .    .....  416 

c           (  Tilletia  fastens  (B.  &  C.)  Trel  ...............  379 

\Tilletia  Tritici  (Beij.)  Wint  ...........    ....  380 

Smut,  loose,  Ustilago  Tritici  (Pers.)  Jens  .............  375 

Wild  Rosemary  (Ledum  palustre  L.) 

Sclerotial  Disease,  Sclerotinia  heteroica  Wor.  &  Nawasch  .......  195 

Wild  Rye  (Elymus  spp.) 

Rust,  Puccinia  graminis  Pers  ..................  408 

Willow  (Salix  spp.) 

Black  Spot,  Rhytisma  Salicinum  (Pers.)  Fr.     ...........  209 

Crown  Gall,  Pseudomonas  tumefaciens  Erw.  Smith  &  Townsend      .     .     .  114 

Decay,  or  Brown  Rot,  Polyporus  sulphureus  (Bull.)  Fr  ........  457 

Powdery  Mildew,  Uncinula  Salicis  (De  C.)  Wint  ..........  230 

White  Rot,  Polyporus  squamosus  (Huds.)  Fr  ............  453 


GENERAL  INDEX1 


Abies  balsamea  467 

Acacia  393 

Acer  139,  185,  208,  231,  335,  454;  sac- 

charum  453,  466,  467 
Actinonema  Rosae  357 
Aderhold,  R.  187,  263,  264 
^Ecidium,  Berberidis  80;  Oxalidis  415; 

punctatum  418 
/Esculus  185,  345 
Agar  agar  26 
Agaricaceae  442 
Agaricus  campestris  39,  56,  72 
Agropyron  410;  repens  410 
Agrostis,    canina    410;     scabra    410; 

stolonifera  410 
Albuginaceae  148 
Alcohol,  fixing  agent  42 
Aleyrodes  214 
Algae  136 

Allium  393;  Cepa  162,  304,  381 
Alnus  185 

Alopecurus  pratensis  410 
Alternaria  288 ;    Brassicae  308 ;   Panax 

305  ;  Violae  308 
Althaea  rosea  419 
Amarantaceae  152 
Ambrosia  381 
Amelanchier  423 

Ammoniacal  copper  carbonate  89 
Ampelopsis,  quinquefolia  314  ;  Veitchii 

347 

Amphicarpa  monoica  139 
Anaerobic  bacteria,  sterilization  18 
Anatomical  effects  5 
Anchusa,  arvensis  416;  officinalis  416 
Ancylistales  135 
Andromeda  ligustrina  441 
Andropogon  378 
Anemone  422;  coronaria  418;    nemo- 

rosa  20 I 

Angular  leaf  spot,  cotton  121 
Anthracnose,  beans    322 ;    clover   and 

alfalfa  328 ;  cotton  325 ;  currants  204; 

grape  332  ;  raspberry  and  blackberry 

334 ;  snapdragon  329 


Antirrhinum  majus  329,  345 

Apium  graveolens  312,  361,  447 

Aralia  quinquefolia  211 

Aristida  378 

Armillaria  mellea  322,  473 

Arthur,].  C.   121,  299,  339,  376,  384, 

388,  407,  414,  421,  435 
Ascomycetes  95,  174,  285,  331 
Asparagus,    capsicus    405 ;    maritimus 

405  ;  officinalis  403,  444,  478 
Aspergillus  56;  flavus  71  ;  niger  71 
Aster  381,  435 
Atkinson,  G.  F.  79,  141,  175,  233,  312, 

313,  321,  325,  335,  399,  444,  452,  457, 

463,  464,  479 
Atriplex  140 
Atwood,  G.  G.  434 
Autobasidiomycetes  439 
Autoclave  19 
Autoecism  387 

Avena,fatua372;  531^372,412,416,420 
Azotobacter  chroococcum  74 

Bacillus  103, 1 06;  amylovorus  107,  121 ; 
anthracis  71  ;  aroideae  107, 133;  caro- 
tovorus  107,  131  ;  Cubonianus  107, 
134;  Hyacinthi-septicus  107,  134; 
prodigiosus  33 ;  solanacearum  107, 
134;  tracheiphilus  107,  129 

Bacteria  82,  103;  elimination  of  36; 
staining  52 

Bacteriaceae  105,  106 

Bacterium  teutlium  106 

Bain,  S.  M.  85,  328 

Bandi,  W.  430 

Bark  disease,  chestnut  281 

Basidiomycetes  56,  95,  285,  439 

Beach,  S.  A.  119,  248,  264,  322,  361 

Begonia  211  ;  rubra  211 

Benecke,  W.  62 

Berberis  vulgaris  410 

Bergamot  oil  52 

Berkeley,  M.  J.  I,  180,  445 

Beta,  cycla  309;  vulgaris  140,  291,  309, 
446,  449,  478 


1  For  common  names  of  host  plants  and  a  list  of  the  diseases  of  any  host,  see  Host 
Index,  page  483. 

499 


500 


GENERAL  INDEX 


Betula  201,  464,  467  ;  lutea  466 

Bidens  161 

Bioletti,  F.  T.  229 

Black  knot,  plums  248 

Black  rot,  cabbage   107;    grapes  254; 

pomaceous  fruits  350;  sweet  potato 

348 

Black  rust,  grain  408 
Black  spot,  maple  208 
Blackman,  V.  H.  384 
Blair,  J.  C.  271 
Blight,  bean  119;  canker  128  ;  ginseng 

3°5 

Bolley,  H.  L.  319,  408 
Bonnet  n 
Boraginacese  139 
Bordeaux  mixture  7,  88,  92 
Botrytis   56,  69,  186,  287  ;    cinerea  66, 

67*  75>  197;  Douglasii  196;  vulgaris 

7i»  197 
Bouillon  24 
Brassica,  campestris  99,  109,  149,  162, 

291;    nigra  149;    oleracea   99,    107, 

308,  449;  Rapa99,  149 
Brefeld,  O.  3,  12,  94,  247,  370,  375»439» 

461 

Bremia  148  ;  Lactucae  164 
Briggs,  L.  J.  210 
Britton,  W.  E.  22 
Bromus  secalinus  410 
Brooks,  Charles  341 
Brooks,  F.  T.  196 
Brown  rot,  conifers  467  ;  lemon  145 ; 

stone  fruits  6,  187 
Brown  rust,  wheat  and  rye  416 
Bud  rot,  carnations  293 
Buller,  A.  H.  R.  453 
Bulliard,  P.  i 

Bundle  blight,  sugar  cane  120 
Bunt,  wheat  379 

Burrill,  T.  J.  3,  in,  121,  215,  271 
Burt,  E.  A.  50,  85 

Callistephus  hortensis  320,  435 

Canker,  blister  282;  body  123;  Euro- 
pean apple  242  ;  larch  202  ;  woody 
plants  239 

Capsella  162;  Bursa-pastoris  99,  149 

Capsicum  annuum  330 

Carbon,  nutrition  73 

Carleton,  M.  A.  408 

Carpinus  185 

Carya472 

Castanea,  crenata  281;  dentata  114, 
281,  336 

Catalpa  347 

Cedar  apples  425 

Cenchrus  378 


Cephalothecium  287  ;  roseum  295 

Ceratiomyxa  101 

Cercis  canadensis  283 

Cercospora  288,  303,  314;  Apii  312, 
361  ;  Beticola  309 ;  Cerasella  263 ; 
circumscissa3i4 ;  Diospyri3i5;  Gos- 
sypina3i3;  Nicotianae  315  ;  sordida 
315;  Violae3i5;  Viticola  314 

Cercosporella  288, 290, 297;  Persicae  297 

Chamberlain,  C.  J.  41 

Chenopodiaceae  164 

Chenopodium  140 

Chester,  F.  D.  103,  201,  299,  301,  330 

Christman,  A.  H.  384,  395 

Chrom-acetic  solution  43 

Chromic  acid  43  ;  cleaning  mixture  13 

Chrom-osmo-acetic  solution  44 

Chrysanthemum  343,  364,  421  ;  frutes- 
cens  117;  indicum  421  ;  sinense  421 

Chrysomyxa   389,    390 ;    Rhododendri 

432 

Chytridiales  63,  136,  139 
Cirsium  arvense  422 
Citrullus   vulgaris   129,    159,   233,  300, 

33°>  449 

Citrus  144,  213,  327 
Cladosporium  287  ;    carpophilum  299  ; 

Cucumerinum  300 ;  fulvum  300 
Clark,  J.  F.  55,  85 
Classification,  general  93 
Clasterosporium  carpophilum  337 
Claviceps  232  ;    purpurea   244 ;    micro- 

cephala  247  ;  setulosa  247 
Climatological  factors  66 
Clinton,  G.  P.  158,  165,  171,  199,  210, 

264,  271,  356,  367,  370,  427,  435,  444 
Clitocybe  443  ;  parasitica  471 
Close,  C.  P.  221 
Clove  oil  51 

Club  root,  cabbage,  etc.  5,  97 
Cobb,  N.  A.  120,  263,  357,  469 
Coccus  103 

Cochlearia  Armoracia  149,  211,  308 
Ccenocentrum  151 
Coffea  arabica  393 
Cohn,  F.  10,  17 
Cold  water  box  29 
Coleosporiaceae  389 
Coleosporium  389,390,435;  Solidaginis 

435 
Colletotrichum  289, 330, 332 ;  Antirrhini 

329  ;  falcatum  330 ;    Glceosporioides 

327  ;  Gossypii  325  ;  Lagenarium  330  ; 

Lindemuthianum  322;    nigrum  330; 

Phomoides  330 ;  Trifolii  328 
Collodion  32 
Colony  counting  36 
Combs  203 


GENERAL  INDEX 


501 


Comes,  O.  3,  93,  477 

Compositae  152,  161,  164,  435 

Conifers  454,  463 

Coniothyrium  290  ;  Fuckelii  354 

Control,  measures  7  ;  methods  85 

Convolvulaceae  152 

Cooke,  M.  C.  94 

Coplin's  staining  jars  48 

Corda,  A.  C.  i,  94 

Cordyceps  232,  286 

Cordyline  347 

Cornu,  M.  3,  152 

Corrosive  sublimate  43,  91 

Corticium  442 ;  vagum  var.  Solani  79, 

212,444,478 

Coryneum  289  ;  Beijerinckii  336 
Cover  glasses, 'cleaning  14,  15 
Craig,  John  295 
Crataegus    123,    423;    monogyna   426; 

Oxyacanthae  426 ;  tomentosa  426 
Crocus  478 
Cronartiaceae  389 

Cronartium  389,  390 ;  Ribicola  433 
Crop  rotation  87 
Crops,  annual  losses  7 
Crown  gall,  almond,  apple,  etc.  114 
Cruciferae  98,  141,  161 
Cucumis,   Melo  300;  sativus  129,  141, 

1 59>  330 

Cucurbita  Pepo  449 
Cucurbitaceae  129,  159,  228 
Cugini,  G.  161 

Culture  media,  preparation  23 
Culture  methods  9 ;   development  and 

application  of  10 
Culture  room  60 
Cultures,    sealing   39 ;    by  sporophore 

fragments  39  ;  storage  38 
Cupressus  423 
Cyclamen  211 

Cydonia  vulgaris  123,  365,  423,  426 
Cylindrosporium    289,   314;     Chrysan- 

themi  343  ;  Padi  314,  339  ;  Pomi  341 
Cystopus,  candidus65,  81, 149, 157, 162; 

convolvulacearum  152  ;  BlitiSi,  152  ; 

Tragopogonis  152 
Cytospora  282 

Dactylis  glomerata  410,  420 
Damping-off  141,  446 
Dangeard,  P.  A.  370,  393 
Darwin,  Charles  168 
Dasyscypha  185;  Willkommii  202 
Datura  Stramonium  302 
Daucus  Carota  131,  291,  449,  478 
Davis,  B.  M.  149 

De  Bary  2,  12,  56,  69,  72,  94,  147,  165, 
186,  197,  215,  244,  370,  397,  398,  408 


De  Candolle  444,  477 

Decay,  or  brown  rot  457 

Deciduous  trees  458,  466 

Dematieae  287 

Dematophora  necatrix  321 

Detmers,  Freda  334 

Dianthus   Caryophyllus  293,  317,  321, 

363.  399.  478 

Diaporthe  254,  290;  parasitica  281 

Diatrypaceae  175 

Dietel,  P.  370 

Diospyros  virginiana  315 

Discomycetes  174,  185 

Disease,  control  3  ;  European  root  477 

Division  of  botany  4 

Dolichos  ornatus  397 

Dothidiaceae  175,  248 

Dothiorella  364 

Downy  mildew  148  ;  crucifers  161  ;  cu- 
cumbers 158  ;  grape  152  ;  lettuce  164; 
lima  beans  170;  onion  162,  304 

Dracaena  347 

Drop,  lettuce  198 

Dry  rot,  potatoes  317  ;  sweet  potatoes 
344 

Dudley,  W.  R.  204,  261,  419 

Duggar,  B.  M.  55,  71,  264,  312,  358,  361, 

365»  444 
Durand,  E.  J.  239 

Early  blight,  celery  312  ;  potato  301 

Echinochloa  crusgalli  378 

Edgerton,  C.  W.  271,  278,  331 

Edson,  A.  W.  254 

Ellis,  J.  B.  94 

Elymus4io;  arenarius  410;  virginicus 

244 

Empetrum  nigrum  195 
Empusa,  Muscae  77 
Engler,/A.  94 
Entomophthorales  136 
Entomosporium  290 ;  maculatum  365 
Entyloma  372,  380 ;  compositarum  381  ; 

Physalidis  380 ;  Ranunculi  381 
Environmental  factors  62 
Epidemics  6 
Ergot  244 

Ericaceae  74,  209,  439,  440 
Erigeron  381 
Eriksson,  J.  3,  57,  201,  221,  384,  408, 

415,416 

Erysiphaceae  63,  77,  81,  175,  209,  215 
Erysiphe  221  ;  Cichoracearum  217,  228; 

graminis  79,  80,  216,  217  ;  Polygoni 

217,  227 

Eschenhagen,  F.  75 
Essary,  S.  H.  328 
Euchlaena  luxurians  377 


502 


GENERAL  INDEX 


Euphorbia  223,  402  ;  Cyparissias  398 
Eustace,  H.  J.  165,  295,  301 
Everhart,  B.  M.  94 
Exoascaceae  63,  77,  81,  175 
Exoascus  175;  Cerasi  185;  deformans 

176;  Pruni  183 
Exobasidiaceae  439 
Exobasidiales  439 
Exobasidium    439  ;    Andromedae   440 ; 

Azaleae  440 ;  Oxycocci  440 ;  Vaccinii 

440 
Eycleshymer,  A.  C.  97 

Facultative  parasites  63 

Fagopyrum  esculentum  297 

Fagus  173  ;  grandifolia  466,  467 

Fairchild,  D.  G.  226,  365 

Falck,  R.  370,  375 

Farlow,  W.  G.  3,  94,  136,  147,  152,  158, 

213,  248,  422,  427 
Farneti,  R.  297 
Faurot,  F.  W.  194 
Ferguson,  M.  C.  55,  60,  72 
Ferrouillat,  P.  254 
Fertilization  tube  143 
Festuca  sylvatica  420 
Ficus  carica  393 
Fisch,  C.  244 
Fischer  de  Waldheim  370 
Fischer,  E.  196,  209,  384 
Fission  fungi  103 
Fixing  solutions  41  ;   chrom-acetic  43  ; 

chrom-osmo-acetic   (Flemming)  44; 

mercuro-nitric  45 
Flasks,  cleaning  14 
Floyd,  B.  F.  367 
Fly  speck,  apple,  etc.  367 
Fomes  443,  464 ;  applanatus  464,  467  ; 

fomentarius  464,  467  ;  igniarius  464, 

465  ;  Pinicola  464,  467 
Formalin  91 
Fragaria  139,  226,  261 
Frank,  B.  3,  93,  343,  477 
Fraxinus  454,  458  ;  americana  464 
Freeman,  E.  M.  93,  375,  416 
Frenching  234 
Fries,  E.  i 
Froehlich,  H.  74 
Fruit  spot,  apple  341 
Fuckel,  L.  i 

Fulton,  H.  R.  297,  322,  469 
Fungi,  classes  of  94;  imperfecti  285 
Fungicides  7  ;  application  of  87  ;  prep- 
aration of  88 
Fusarium  288,  303,  320;  Lini  319;  Ly- 

copersici  318;  oxysporum  239,  317 
Fusicladium,  dendriticum  264 ;  Pyrinum 

264 


Gall,  cranberry  138;  heaths  440 

Galloway,  B.  T.  4,  229,  301 

Garman,  H.  107 

Gaylussacia  440 

Gelatin,  nutrient  29 ;  sterilization  20 

Gelidium  26 

Germination  8  ;  methods  57  ;  require- 
ments 55  ;  studies  55 

Geyler,  H.  439 

Glceosporium  79,  205,  288,  303,  330; 
ampelophagum332  ;  apocryptum335; 
cingulatum  331  ;  fructigenum  331  ; 
Juglandis  335;  laeticola  335;  Ligus- 
trinum  335  ;  nervisequum  279,  331  ; 
Ribis  205,  331  ;  Tiliae  335  ;  Venetum 

334 

Gloiopeltis  26 
Glomerella  254,  331  ;  rufomaculans  36, 

271,  289,  334 
Glyceria  nervata  244 
Glycerin  agar  28 
Gnomonia254;  leptostyla  336 ;  Veneta 

278 

Gnomoniaceae  175,  254 
Gnomoniella  circinata  205 
Gorham,  F.  T.  104 
Gossypium  121,  233,  296,  304,  313,  325, 

445,  479 ;  hirsutum  449 
Grafting  wax  83 
Granville  tobacco  wilt  134 
Grout,  A.  J.  301 
Guignardia    254,    290;    Bidwellii    254; 

Vaccinii  259 

Gymnoconia  389,  390 ;  Peckiana  427 
Gymnosporangium  80,  389,  422  ;  clava- 

riaeforme  426 ;  globosum  426 ;  macro- 
pus  425 ;   Sabinae  426 

Halsted,  B.  D.  97,  158,  171,  243,  248, 
271,  3T7>  336»  343'  344,  345'  346,  347, 
348,  350,  403 

Hanging-drop  culture  57  ;  rings  for  59 

Harding,  H.  A.  107,  131 

Harper,  R.  A.  52,  136,  215,  370 

Harrison,  F.  C.  131 

Hartig,  R.  3,  93,  173,  202,  242,  280,  321, 

467,  473 

Hasselbring,  H.  282,  332 
Heald,  F.  D.  244,  293 
Heart  rot,  beets  343 ;  sugar  maple  452 
Hedgcock,  G.  G.  114 
Hedrick,  U.  P.  85 
Heinz,  A.  134 
Helianthus,  annuus  141,  161,  420;  tu- 

berosus  161,  420 
Helminthosporium   288 ;    carpophilum 

337 
Helotiaceas  175,  203 


GENERAL  INDEX 


503 


Hemibasidiomycetes  370 

Henning,  E.  408,  415 

Ilennings,  P.  433 

Hepatica  acutiloba  418 

Hesse  141 

Heteroecism  387 

Hieracium  422 

Hitchcock,  A.  S.  376 

Holway,  E.  W.  D.  407,  417 

Hordeum  218,  377,  410  ;  bulbosum  218  ; 
decipiens  218;  distichum  218;  hexa- 
stichum  218;  intermedium  218;  ju- 
batum  218;  murinum  218;  secalinum 
218;  sylvaticum  218;  vulgatum  218; 
vulgare  410;  Zeocriton  218 

Howard,  A.  469 

Howell,  J.  K.  395 

Humphrey,  J.  E.  158,  187,  198,  248 

Hyacinthus  orientalis  120 

Hydnaceae  442 

Hydnum443;  coralloides453;  erinaceus 
453 ;  septentrionale  452 

Hymenomycetales  441 

Hymenomycetes  72 

Hypertrophies  5 

Hyphomycetes  49,  285 

Hypochnus  451 

Hypocreaceae  175,  232,  248 

Hypocreales  247 

Iberis  umbellata  99 

Imbedding  45 

Indicators,  titration  33 

Infection,  artificial  8,  76 

Infiltration  45 

Insect  breeding  cage  82 

Introduction  I 

Ipomoea  Batatas  243,  344,  348,  449,  479 

Isaria  286 

Isolation  9;  colony  36;  cultures  9,  10, 

12,  34,  35  ;  materials  34  ;  series  36 
Istvanffi,  G.  de  196 

Jackson,  H.  S.  85 

Jacky,  E.  421 

Jaczewski,  A.  V.  254 

Jahn,  E.  101 

Jensen,  J.  L.  372 

Johnson,  E.  C.  375 

Jones,  L.  R.  121,  131,  165,  301 

Juglans,   cinerea  331,  335,  458;   nigra 

114,  458  ;  regia  120 
Juniperus  423  ;  barbadensis  463  ;  com- 

munis  426;  virginiana  423,  425,  426, 

463 

Karsten,  P.  A.  I 
Kellerman,  W.  A.  372,  379 


Kissling,  E.  196 

Klebahn,  H.  204,  208,   278,  336,  384, 

398,4i5>433 
Klebs,  E.  10 
Knot,  olive  118 
Knowles,  E.  L.  376 
Koch,  R.  10,  1 6,  76 
Kriiger,  F.  343 

Kiihn,  J.  3,  67,  93,  399,  445,  477 
Kusano,  S.  136,  421 
Kiister,  E.  5 


Labiatae  407 

Lablab  vulgaris  398 

Lactuca  164;  sativa  196,  198,  363,  446, 

449 

Lafar,  Fr.  94 

Larix  decidua  202,  458,  463,  467 
Late  blight,  celery  361  ;  potato  165 
Lathyrus  pratensis  398 
Laubert,  R.  335 
Lautenschlager,  sterilizer  21 
Lawrence,  W.  H.  264 
Leaf  blight,  cotton  313  ;  cranberry  338  ; 

pear  and  quince  365  ;  tomato  362 
Leaf  blotch,  rose  357 
Leaf  curl,  peach  176 
Leaf-splitting  blight,  sugar  cane  263 
Leaf  spot,  alfalfa  203  ;  beets  309  ;  pear 

358;  strawberry  261 
Ledum  palustre  195 
Lee,  A.  B.  41 
Leersia  380 
Lepidium  sativum  141 
Leptosphaeria  circinans  479  ;  Coniothy- 

rium  356 

Leptothyrium  290  ;  Pomi  367 
Lesions  ,5 
Leveille>  J.  H.  i 
Lewton- Brain,  L.  330 
Light,  relation  of  fungi  68,  71 
Ligustrum  vulgare  331 
Lilium  196 

Lime-sulfur  wash  90,  92 
Linum  319 
Liquid  media  23 
Lister,  Jos.  10 
Litmus  milk  25 
Lodeman,  E.  G.  85,  248 
Loeffler,  Fr.  9 
Lolium  perenne  244 
Lupinus  albus  211  ;  angustifolius  211; 

luteus  211  ;  thermis  211 
Lustner,  G.  147 
Lycopersicum  esculentum  134,  300,302, 

318,  330,  362,  449 
Lysigenous  cavity  137 


504 


GENERAL  INDEX 


Macchiati,  L.  134 

Macrosporium  286 ;  Catalpae  347 ;  Iridis 

304;  nigricantium  79,  304;  Sarcinula 

304;    Solani   301;    Tabacinum   304; 

Tomato  304 

Magnolia  grandiflora  347 
Magnus,  P.  140 
Malvaceae  419 
Manure  decoctions  24 
Marasmius  443  ;  plicatus  469 ;  Sacchari 

469 
Marsonia    289,    336;    Juglandis    336; 

ochroleuca  336;  Populi  336 
Massee,  G.  93 
Mathiola  incana  99 
Mayr,  H.  239 

McAlpine,  D.  337,  384,  399,  408,  417 
Meat  extracts  25 
Media,  sterilization  15 
Medicago  sativa  140,  203,  328,  477,479 
Melampsora  389,  390 ;  Larici-tremulae 

437 ;    Magnusiana    437 ;    Pinitorqua 

437  ;  Rostrupii  438  ;  tremulae  437 
Melampsoraceas  389 
Melanconiales  286,  288 
Meliola  Camelliae  213 
Metcalf,  Haven  281,  297 
Microsphaera  221  ;  Alni  228 
Migula,  W.  103 
Mildew   (powdery),   apple  and    cherry 

226;    composites    228;    gooseberry 

221;    peach  224;    grapes   229,  357; 

peas   227 ;   willow  and   poplar   230 ; 

trees  231 ;  woody  plants  228 
Miles,  G.  F.  479 
Milk  25;  sterilization  20 
Millardet,  A.  3,  85,  158 
Miyabe,  K.  304 
Miyake,  K.  141 
Moisture,  relation  of  fungi  66 
Mold,  onion  304 
Mollisiaceas  175,  203 
Monilia  186,  286 
Monoblepharidales  135 
Morphology  2 
Morse,  W.  J.  131 
Morus  134 
Mucedineae  286 
Mucor  23  ;  mucedo  64 
Mucoraceae  49,  56 
Mucorales  135 
Mtiller,  J.  208 
Murrill,  W.  A.  281 

Mycological  advances  12;  relations  4 
Mycology,  systematic  i 
Mycorhiza,  endophytic  75 
Mycosphaerella    254;     Cerasella    263; 

Fragariae  261,  296;  stratiformans,  263 


Mycosphaerellaceae  175,  254 
Myxomycetes  95,  97 
Myxosporium  279 

Nawaschin,  S.  97,  195 

Nectria  232  ;  cinnabarina  239 ;  ditissima 

240,  242  ;  Ipomoeae  243 
Nees  von  Esenbeck,  C.  G.  i 
Neger,  F.  W.  215 
Nemophila  auriculata  211 
Neocosmospora  232;  vasinfecta  83,  233, 

320 

Nerium  Oleander  118 
Neutralization,  culture  media  33 
Newcombe,  F.  C.  427 
Nicotiana  Tabacum  134,  210,  304,  315 
Nitrogen,  relation  of  fungi  73 
Nordhausen,  M.  196 
Norton,  J.  B.  S.  187,  376 
Nowakowski,  L.  136 
Nummularia  254  ;  discreta  282 
Nutrient  salt  solution  28 
Nutrients,  relation  of  fungi  73 

Obligate  parasites,  63 ;  saprophytes  63 

O'Brien,  Abigail  71 

OZdocephalum  albidum  56 

OZnothera  biennis  139 

Oidium  218,286,480;  Tuckeri  229,286 

Olea  europaea  118 

Olive,  E.  W.  101,  384,  394,  408 

Onobrychis  Cristagalli  211 

Onygena  corvina  56 

Oochytriaceae  139 

Oospora  286 ;  scabies  290 

Orange  rust,  aster  and  golden-rod  435  ; 

blackberry  and  raspberry  427 
Orchidaceae  75 
Orton,  W.  A.  233 
Oryza  sativa  247,  297,  380 
Ostrya  virginiana  473 
Oudemans,  C.  A.  J.  A.  3 
Oxalis  415 
Ozonium  auricomum  480;  omnivorum 

479 

Paddock,  W.  334,  350 

Palla,  E.  231 

Pammel,  L.  H.  107,  309,  363,  395,  422, 

444»  479 

Panax  quinquefolium  211,  305,  320 
Panicum  378  ;  sanguinale  298 
Paraffin  process  45 
Parasitism  62 
Paris  green  92 
Pasteur,  L.  n 
Pastinaca  sativa  291,  312 
Pathology,  practical  3 


GENERAL  INDEX 


505 


Patterson,  Flora  W-.  175 

Peniclllium  23,  56,  71,  145;  glaucum  69 

Peridermium  436 ;  acicolum  436 ;  strobi 

433 

Penplasm  143 
Perisporiacese  175 
Perisporiales  209 
Peronospora  148 ;  parasitica  161 ;  Schlei- 

deniana  162;  sparsa  164 
Peronosporaceae  49,  63,  72,  77,  148 
Peronosporales  55,  136,  140,  141,  147 
Persoon,  C.  H.  I 
Pestalozzia  289  ;  Guepini  338  ;  Hartigii 

339 

Petri,  L.  118 
Petri,  R.  J.  10 
Petunia  69 
Phacidiaceae  175,  207 
Phaseolus  119,  227;   lunatus  171;  vul- 

garis  397,  449 
Phleum  pratense  244,  415 
Phlox  228    • 
Phoma  260,  289  ;  Batatas  344  ;  Betae  74, 

343;  radicis74;  Solani345;  uvicola256 
Phragmidium    389,   390 ;    subcorticium 

43° 

Phyllachora  Trifolii  298 
Phyllactinia  221  ;  Corylea  231 
Phyllosticta  260,  289,  314,  345;  Ampe- 

lopsidis  347  ;  Catalpae  347  ;  hortorum 

346;    Labruscae   256;    limitata  352; 

maculicola  347  ;   Paviae  345  ;    Pyrina 

347,  352  ;  solitaria  346;  tabifica  344; 

Violas  347 

Physalis  pubescens  380 
Physiological  relations  5,  55 
Physiology  2 
Phytomyxaceas  97 
Phytomyxales  97 
Phytophthora  63,  67, 147, 148;  cactorum 

173;  infestans  65,  72,  165;  Phaseoli 

171 

Picea  458,  463,  467  ;  excelsa  432 
Pierce,  N.  B.  118,  120,  176,  315 
Pink  rot,  apple  295 
Pinus  173,  339,  463,  467  ;  cembra  434; 

rigida  436 ;    strobus  433  ;    sylvestris 

436 

Piricularia  287  ;  grisea  297  ;  Oryzae  298 
Pisum   arvense  398;  sativum  211,  227, 

398,  449 

Plant  decoctions  23 
Plant  pathology,  rise  of  2  ;  section  of  3  ; 

modern  4 
Plantaginaceas  164 
Plasmodiophora  97  ;  Brassicae  97 
Plasmopara  cubensis  1 58  ;  Viticola  65, 

152 


Platanusoocc'identalis  278 

Platinum  needle  35 

Plectascineae  209 

Pleospora  herbarum  304 

Plepsporaceae  175,  254 

Pleurotus  ostreatus  38 

Plowright,  C.  B.  370,  384 

Plowrightia  morbosa  248 

Plum  pockets  183 

Poa  217  ;  compressa4io  ;  pratensis  247 

Podosphaera  221  ;  leucotricha  224,  226; 
Oxyacanthas  226 

Polygonum  393 

Polyporaceas  442 

Polyporus  443  ;  Betulinus  464  ;  borealis 
463;  carneus463;  Fraxinophilus464; 
Juniperinus  463  ;  Schweinitzii  463  ; 
squamosus  453  ;  sulphureus  39,  457 

Polythrincium  287,  298  ;  Trifolii  298 

Pomeae  423 

Populus  185,  230,  336,  458;  alba  114; 
tremula  437  ;  tremuloides  438,  466 

Potassium  sulfide  90 

Potato  disease  165 

Potter,  M.  C.  131 

Powell,  G.  H.  367 

Prillieux,  Ed.  3,  93,  280 

Pritchard,  F.  J.  408 

Protobasidiomycetes  384 

Protozoa  136 

Prucha  107 

Pruning  128 

Prunus  114,  185,  187,  226,  263,  314,  458, 
471;  americana  249,339,417;  Amyg- 
dalus  1 1 6,  315,  417  ;  Armeniaca  116, 
188,  249,  299,  335,  417;  avium  185, 
249,  473;  Cerasus  185,  249;  domes- 
tica  183,417,473;  pennsylvanica249', 
Persica  114,  176,  187,  224,  335,  336, 
417;  £erotina  249,417  ;  virginiana  249 

Pseudomonas  106;  campestris  67,  105, 
107;  Hyacinthi  106,  in,  120;  Jug- 
landis  106,  120;  malvacearum  106, 
120;  Oleas  106,  118;  Phaseoli  106, 
119;  Pruniio6;  radicicola  73  ;  Stew- 
artii  106,  in,  120;  Syringas  107; 
tumefaciens  114;  vascularum  106, 
120 

Pseudopeziza  203,  331  ;  Medicaginis 
203 ;  Trifolii  204 

Puccinia  389,  390;  Asparagi  403;  Chrys- 
anthemi42i  ;  coronata42o;  dispersa 
416;  fusca  422  ;  glumarum4i6;  gra- 
minis  80, 408  ;  Helianthi  420 ;  Hiera- 
cii  422;  malvacearum  419;  Menthas 
407;  Peckiana  430;  Phlei-pratensis 
415;  Pruni-spinosas  417;  purpurea 
414;  rubigo-vera  416;  Sorghi  414; 


GENERAL  INDEX 


suaveolens42i  ;  Tanaceti  420 ;  Trag- 

opogi  421  ;  Violae  407 
Pucciniaceae  389 
Pueraria  137 
Pure  cultures,  establishing  37  ;  methods 

9 

Puriewitsch,  K.  74 
Pycnochytrium  138;  aureum  139;  glo- 

bosum  139:  Myosotidis  139 
Pyrenomycetes  174 
Pyrus  114,  123, 185,  423;  Aucuparia  195, 

426;  communis  1 16, 1 23, 264, 358, 365, 

426,458;  coronaria  425  ;  Malus  123, 

226,  239,  242,  264,  271,  341,  346,  347, 

350,  367,  425,  426,  458,  471 
Pythiaceas  140 

Pythiacystis  141,  148;  Citrophthora  144 
Pythium    78,    141,    148,    151,    446;    de 

Baryanum  141,  157,  173 

Quaintance,  A.  L.  187 

Quercus  185,  280,  454,  458,  466,  471; 

alba  278,  473;    coccinea  278;    velu- 

tina  278 

Radicula     Nasturtium-aquaticum    141, 

149 
Ramularia  287,  296;  areola  296;  rufo- 

maculans  297  ;  Tulasnei  262,  296 
Ranunculaceae  381 
Raphanus  sativus  99,  149,  162,  449 
Rathay,  £.175 
Reddick,  D.  254 
Reed,  G.  M.  215,  217 
Reed,  H.  S.  320 
Resin  wash  215 
Resistant  varieties  85 
Rhizoctonia   78,  210,  444,  478;    Betae 

445  ;  Medicaginis  446,  477 
Rhizopus  nigricans  71,  349 
Rhododendron  hirsutum  196,  432  ;  fer- 

ruginium  196,  432 
Rhytisma    Acerinum    208 ;    Salicinum 

209 ;  Vaccinii  209 
Ribes  204,  221,  240,  363,  364,  393,  433  ; 

aureum  435;    irriguum  435;  nigrum 

435  ;  rub  rum  435 

Richards,  H.  M.  384,  422,  427,  440 
Robinia  Pseudo- Acacia  458 
Robinson,  B.  L.  175 
Rcestelia  Pyrata  425 
Rolfs,  F.  M.  444 
Rolfs,  P.  H.  327 
Root  disease,  sugar  cane  469 
Root  rot,  alfalfa,  cotton,  etc.  479 ;  fruit 

trees  471  ;  tobacco  210;  vine  321 
Root  and  stem  rot  fungus  444 
Rorer,  J.  B.  346,  352 


Rosa  114,  164,  224,  357,  430 

Rosaceae  114,  139 

Rosellinia  254  ;  Quercina  280 

Rostowzew,  S.  J.  147 

Rubus  114,  139,  334,  354,  363,  427 

Rumex  402 

Russell,  H.  L.  107 

Rust,  apple  425  ;  beans  397  ;  carnation 
399  ;  clover  395  ;  currant  423  ;  fungi 
384;  hollyhock  419;  maize  414;  mint 
407  ;  poplar  437  ;  rhododendron  and 
Norway  spruce  43 2;  roses  430;  stone 
fruits  417;  timothy  415;  vetch  and 
garden  pea  398  ;  violet  407 

Rytz,  W.  136 

Saccardo,  P.  A.  I,  94 

Saccharum  officinarum  120,  263,  330, 
469 

Sadebeck,  R.  175 

Saida,  K.  74 

Salix  114,  209,  230,  454,  458 

Salmon,  D.  E.  244 

Salmon,  E.   S.  79,  215,  221,   228,   231 

Sands,  M.  C.  215 

Sanitary  environment  7 

Sappin-Trouffy  393 

Saprolegniaceas  49 

Saprolegniales  136 

Sa^prophytism  62 

Savastano,  L.  118 

Scab,  apple  264 ;  peach  and  apricot  299; 
pear  264  ;  potato  290 

Scald,  cranberry  259 

Schizomycetes  95,  103 

Schrenk,  H.  von  114,  271,  457,  463,  464 

Schroeter,  J.  3,  94,  136,  147,  175 

Schweinitz,  L.  I),  i 

Sclerospora  148,  161;  graminicola  161 ; 
macrospora  161 

Sclerotinia  185,  186;  Aucupariae  186, 
195;  baccarum  186, 195  ;  Betulae  186, 
201;  cinerea  187;  fructigena  186, 
187,  286;  Fuckeliana  186,  196;  het- 
eroica  186,  195;  Libertiana  186,  198, 
201  ;  megalospora  186,  195 ;  Oxy- 
cocci  186,  195;  Rhododendri  186, 
196;  Trifoliorum  186,  201;  tuberosa 
186,  201  ;  Vaccinii  186,  195 

Scolecotrichum  287 

Scott,  W.  M.  85,  194,  271,  346,  352 

Scribner,  F.   L.  4,   152,  254,  261,  278, 

3'3>  332,  334,  347,  357,  365,  4'7 
Secale,  217  ;  cereale  217,  244,  383,  410, 

416 

Seed  selection  86 

Seedling  stem  blight,  egg  plant  345 
Selby,  A.  D.  114,  176,  367,  381 


GENERAL  INDEX 


507 


Sempervivum  173 

Senecio  164,  435;  elegans  210 

Separation  cultures  34 

Septogloeum  289 

Septoria  290  ;  Chrysanthemi  364  ;  con- 

similis  363  ;  Dianthi  363  ;  Lycopersici 

362;    Petroselini  312,  361  ;    Pyricola 

358  ;  Ribis  363  ;  Rubi  363 
Setaria  161  ;  crus-ardeae  247 
Seymour,  A.  B.  94 
Shear,  C.  L.  138,  259,  338,  440,  479 
Shot-hole  disease,  plum  and  cherry  339 
Sicyos  angulatus  159 
Siliciate  jelly  28,  31 
Sinapis  99 

Sirrine,  F.  A.  165,  301,  381,  403 
Sisymbrium  officinale  99 
Slides,  cleaning  14 
Slime  molds  97 
Smith,  C.  O.  118 
Smith,  Erw.  F.  9,   103,  104,  107,   in, 

114,  118,  119,  120,  121,  129,  134,  187, 

224,233,317 
Smith,  Grant  215 
Smith,  R.  E.  67,  120,  144,  196,  198,  264, 

336>  403 

Smith,  Theobald  18 
Smith,  W.  G.  93 
Smut,  blue-stem   grass   378 ;    corn    5, 

376;  oats  37  2;  onion  381;  wheat  37  5 
Sodium  silicate  31 
Soft  rot,  calla  133;  carrot  131 
Solanaceae,  wilt  134 
Solanum,    Commersonii    168;    Melon- 

gena    134,    345,    346;     polyadenium 

168;  tuberosum   134,  165,  290,  301, 

444>  449 
Solid  media  26 
Solidago  402,  435 
Solutions,  relation  of  fungi  75 
Sonchus  164 

Sooty  blotch,  apple,  etc.  367 
Sooty  mold,  orange  213 
Sooty  spot,  clover  298 
Sorauer,  P.  3,  93,  187,  366,  444 
Sorbus  283 
Sorghum  377,  414 

Sorosporium  371  ;  Syntherismae  378 
Southworth,  E.  A.  278,  325 
Spallanzani  1 1 
Spaulding,  Perley  271,  434 
Sphaerella  Gossypina  313 
Sphaeriaceae  254 
Sphaeriales  253 
Sphaeronema  fimbriatum  348 
Sphaeropsidales  286 
Sphaeropsis  290,  347  ;  cinerea353  ;  Mali 

353;  Malorum  350,  353 


Sphaerotheca  221  ;  Humuli  226;  Mors- 
uvae22i ;  pannosa  224;  phytoptophila 
81 

Spieckermann,  A.  131 

Spinacia  oleracea  164 

Spirillum  103 

Spongy  dry  rot,  apple  316 

Spontaneous  generation  n 

Spores,  heat  resistance  17 

Sporonema  279 

Sporotrichum  286 ;  globuliferurn  7 1  ; 
Poae  293 

Spraying  7 

Stager,  R.  244 

Staining  48 ;  filamentous  fungi  48 ; 
fleshy  fungi  49 

Stains,  carbol  fuchsin  49,  53 ;  Congo 
red  50 ;  Ehrlich-Biondi-Heidenhain 
50;  Flemming  triple  51;  gentian 
violet  51  ;  iodine  green  53 ;  iron 
haematoxylin  52 ;  Loeffler's  methy- 
lene  blue  53 ;  Magdala  red  50 ; 
Mayer's  paracarmin  50;  nigrosin  51; 
orange  G  50,  51  ;  saffranin  50,  51 

Starch  jelly  29 

Steam  sterilizer  16;  pressure  19 

Stem  rot,  clover  201  ;  sweet  potato  and 
egg  plant  243 

Stereum  443 

Sterilization,  at  100°  C.  16;  hot  air  21 ; 
principles  1 1 ;  principles  and  methods 
15;  soil  21  ;  under  pressure  19 

Stevens,  F.  L.  316 

Stewart,  F.  C.  107,  in,  158,  165,  204, 

293.  3OI»  329»  354,  381,  399»  433 
Stigmatea  Mespili  366 
Stilbeae  303 
Stock  cultures  37 
Stone,  G.  E.  67,  198,  403 
Stoneman,  Bertha  271,  331 
Stuart,  Wm.  165,  372,  376,  399 
Sturgis,  W.  C.  171,  290,  301,  312,  321, 

367,  38i 
Subcultures  37 
Sulfur  90 

Swingle,  D.  B.  317 
Swingle,  W.  T.  85,  147,  372,  375,  379 
Sydow,  P.  384 
Synchytriaceae  136 
Synchytrium   137,  138;  decipiens  138, 

139 ;  fulgens  139 
Synthetic  liquid  media  25 
Syringa  228 

Tavel,  F.  von  95 

Technique  10,  41 ;  fixing  41 ;  imbedding 

45  ;  staining  41  ;  histological  8 
Tecoma  radicans  315 


5o8 


GENERAL  INDEX 


Temperature,  high  70 ;  low  7 1  ;  opti- 
mum 69  ;  relation  of  fungi  69 

Ternetz,  Charlotte  74 

Test  tubes,  cleaning  13 

Thaxter,  R.  162,  171,  210,  290,  381,  422 

Thelephoraceae  442 

Thielavia  basicola  210,  348 

Thuya  occidentalis  463 

Tilia  454  ;   Ulmifolia  335 

Tilletia  372;  foetens  379,  380;  horrida 
380;  Tritici  380 

Tilletiaceae  371 

Titration,  culture  media  33;  Fuller's 
procedure  34 

Tolyposporium  371  ;  bullatum  378 

Tourney,  J.  W.  114 

Townsend,  C.  O.  114,  133 

Trabut,  L.  337 

Tragopogon  421  ;  porrifolius  152,  421 

Trametes  443  ;  Pini  467 

Transfers  37 

Tranzschel,  W.  427 

Traverse,  G.  B.  161 

Trelease,  W.  162 

Trifolium  141,  201,  204,  298,  328,  479; 
carolinianum  396 ;  hybridum  395  ;  in- 
carnatum  395  ;  pratense  298,  395  ; 
repens  395 

Trigonella  ccerulea  211 

Triticum  375,  379,  410,  416 

Tsuga  canadensis  458,  468 

Tubercle  118 

Tuberculariae  288 

Tubeuf,  K.  von  93,  196,  201,  433 

Tulasne,  L.  R.  and  C.  i,  95,  244,  370, 

445'  477 
Tyndall  17 

Ulmus,  185,  454;  americana  283 
Uncinula    221  ;    Aceris    231  ;    necator 

229 ;  Salicis  230 
Underwood,  L.  M.  95 
Unger,  F.  93 
Uredinales    55,    63,    77,   80,    81,    384 ; 

families    and    genera  388 ;    synopsis 

of  species  391 
Urocystis  372  ;    Cepulae   87,   381  ;    oc- 

culta  383 
Uromyces    389  ;    appendiculatus    397  ; 

Betae  399  ;   Caryophyllinus  399 ;  Pisi 

398  ;  Rumicis  402  ;    Solidaginis  402  ; 

scutellatus  402  ;  Trifolii  395 
Urophlyctis    140;    Alfalfae  140;  lepro- 

ides  140;  pulposa  140 
Uschinsky's  solution  26 
Ustilaginaceae  371 
Ustilaginales  63,  77,  370 
Ustilaginoidea  Oxyzae  247 


Ustilago  371;  Avenae  372;  levis  373; 
Reiliana  377  ;  Tritici  375;  Zeae  376, 
378 

Vaccinium  arboreum    209  ;    macrocar- 

pon   259,   338,   440;     Myrtillus    195; 

Oxycoccus  139,  195;  uliginosum  195; 

Vitis-idaea  195,  440 
Valsaceae  254 
Van  Hall,  C.  J.  J.  103,  131 
Van  Tieghem  cell  57 
Vegetable  products  29 
Venturia  254,  287;  Pomi  264;  Pyrina264 
Verbena  227 

Vessels,  sterilization  of  15 
Viala,  P.  152,  229,  254,  321,  332 
Vicia  227  ;  cracca  398 
Vigna  marginata  398 
Viola  139,308,315,  347,407;  odorata2io 
Vitis  114,  152,  229,  254,  274,  314,  321, 

332;    aestivalis    154;    cordifolia   154; 

Labruscas  1  54  ;  vinifera  1  54 
Volutella  288,  332  ;  Dianthi  317  ;  fructi 


Wager,  H.  50,  149 

Waite,  M.  B.  122 

Wakker,  J.  H.  120,  125,  186,  469 

Ward,  H.  M.  71,  93,  141,  165,  197,  381, 

408,  416 
Water  fungi  135 
Water  molds  140 
Water-pore  infections  108 
Webber,  H.  J.  213 
Wehmer,  C.  187,  239 
Whetzel,  H.  H.  119,  122,  162,  305,322, 

397 

Whipple,  O.  B.  224 
White  rot,  deciduous  tress  453 
White  "  rust,"  crucifers  149 
Wiesner,  J.  69 
Wilcox,  E.  M.  471 
Wilson,  G.  W.  147 
Wilt,  cucurbits  129;  cotton,  etc.  233; 

flax  3  19;  Solanaceae  134;  sweet  corn 

in 

Winter,  G.  3,  94 
Witches'  broom  5  ;  cherry  185 
Wither  tip,  citrus  fruits  327 
Woronin,  M.  3,  97,  187,  195,  439 

Xanthium  393 
Xylariaceae  254 

Zalewski,  A.  149 
Zantedeschia  aethiopica  133 
Zea  mays  1  1  1,  141,  161,  376,  414 
Zimmermann,  A.  41 
Zopf,  W.  95,  136,  210 


ANNOUNCEMENTS 


FUNGOUS  DISEASES  OF  PLANTS 

By  BENJAMIN  MINGE  DUGGAR 
Professor  of  Plant  Physiology  in  Cornell  University 


8vo,  cloth,  508  pages,  illustrated,  $2.00 


IN  this  book  are  presented  many  of  the  vital  facts  brought 
to  light  by  modern  research  in  plant  pathology,  which 
should  be  invaluable  to  farmers,  gardeners,  and  every  one 
interested  in  plants.  It  is  of  equal  usefulness  as  a  reference 
book  or  as  a  textbook  for  college  or  university  instruction. 
There  is  embodied  a  comprehensive  discussion  of  the  chief 
fungous  diseases  of  cultivated  and  familiar  plants.  The  value 
of  the  bacteriological  method  in  plant  pathology  is  emphasized 
by  special  chapters  giving  concise  methods  for  the  cultivation 
of  parasitic  fungi.  Important  physiological  relations  of  these 
plants  are  also  presented  in  sufficient  detail  to  give  the  reader 
the  salient  facts  which  have  been  developed. 

The  arrangement  of  topics  is  in  taxonomic  sequence  with 
respect  to  the  fungi,  so  that  morphological  study  is  most  effec- 
tive ;  and,  moreover,  there  is  a  full  treatment  of  pathological 
modifications. 

Each  disease  is  discussed  with  reference  to  its  occurrence, 
the  nature  of  the  lesions  or  processes  jnduced,  the  structure, 
life  history,  and  cultural  relations  of  the  causal  fungus,  and 
practical  methods  for  prevention  or  control. 

The  literature  of  the  subject  is  freely  cited,  and  a  host  index 
provides  a  ready  reference  to  all  of  the  important  fungous 
diseases  occurring  upon  any  host.  The  method  of  treatment 
followed  is  intended  to  facilitate  and  stimulate  the  work  of  the 
student  and  to  enlarge  the  interests  of  the  general  reader. 


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.Davis:  Physical  Geography 1.25 

Davis :  Practical  Exercises  in  Physical  Geography 45 

Duggar :  Fungous  Diseases  of  Plants 2.00 

Gage:   Principles  of  Physics  (Revised  by  Goodspeed)    ....     1.50 

Hastings  and  Beach  :   General  Physics 2.75 

Higgins:  Experiments  in  Physics    ..">'.< 35 

Higgins :  Lessons  in  Physics 90 

Higgins:   Simple  Experiments  in  Physics 35 

Hopkins:  Soil  Fertility  and  Permanent  Agriculture 2-25 

Hough  and  Sedgwick  :   Human  Mechanism 2.00 

Linville  and  Kelly:   General  Zoology 1.50 

McGregory  :  Manual  of  Qualitative  Chemical  Analysis  (Rev.  Ed.)  i.oo 
McPherson  and  Henderson:  Elementary  Study  of  Chemistry  1.25 
Meier :  Herbarium  and  Plant  Description.  With  directions  for 

collecting,  pressing,  and  mounting  specimens 60 

Meier:  Plant  Study 75 

Millikan  and  Gale:   First  Course  in  Physics 25 

Newman:  Laboratory  Exercises  in  Elementary  Physics,  per  doz.       .50 

Norton  :  Elements  of  Geology 40 

Ostwald  and  Morse  :   Elementary  Modern  Chemistry oo 

Pratt:   Invertebrate  Zoology .       .25 

Pratt:  Vertebrate  Zaology 50 

Russell  and  Hastings  :   Experimental  Dairy  Bacteriology    ...       .00 

Sabine  :  Laboratory  Course  in  Physical  Measurements  (Rev.  Ed.)        .25 

Sellers:  Qualitative  Analysis  (Rev.  Ed.) 

Stone  :  Experimental  Physics 

Ward:  Practical  Exercises  in  Elementary  Meteorology       .     .     . 

Wentworth  and  Hill:  Textbook  of  Physics .       .15 

Williams:   Elements  of  Chemistry 10 

Williams:   Essentials  of  Chemistry 25 

Young:   General  Astronomy 2.75 

Young:    Lessons  in  Astronomy  (Rev.  Ed.) 1.25 

Young:   Manual  of  Astronomy 2.25 

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